Setting up a system - What to buy WHEN?

I agree with going to audio shows.  Also, find some friends to borrow gear from.  Once you have the speakers there are many different ways to power them:  tubes, solid state, integrated, power amps, class A, class A/B, class D and more.  You need to make sure that you have enough power to get what you need out of the speakers.
1 watt of distortion will blow any speaker but most speakers can handle hundreds of clean watts.  Low efficiency speakers such as 86 db will take two to four times as much power to hit the same volumes as an efficient speaker rated in the low to mid 90's.  So, if you find out that you love a speaker rated at 83db expect to buy those giant monoblocks.  However, if you fall in love with 99db horns you only need to get 7 watts.
Finally, have a good reliable source that you trust with a couple of recordings that you know well.

Two things stand out to me.  One, decide what your budget is, broken out by component.   Many 4 Ohm speakers require major amounts if power that can be quite costly, ask me how I know, LOL.

I would listen to many speakers and then let them drive the choice of amplifier.

Pre amps are about synergy with the speakers and the power amp for me.

Achieving a balance with regard to the total budget will save lots of $$$s as over spending on one item that is way above the rest of the system is often money spent unwisely.

Most of all, enjoy the process!!!

One point with one amp then strapping it and buying a second to make mono. Most stereo amps will not be happy bridged to mono driving a 4 ohm speaker.

Great point! I was thinking of amps that support this feature only. I've seen the rear of certain amps that have a toggle switch for this kind of mode, and that's what I was thinking of but didn't say it directly.  Thanks!

Wow, Great!
Speakers first it is! Thanks to all who replied with their tips and suggestions. (Especially Big Joe with his 1st, 2nd, 3rd, etc list.)
I've auditioned some speakers and have some more to listen to.
Thanks again, all!

bigslacker

My plan is to hopefully be able to buy an amp that'll power both mains on it's own. Then circle back later, buy another of the same unit. Then I'll swap each over to monoblock mode - one driving each main.

It's really always a compromise to use bridged amplifiers, which is what it sounds like you're planning. A bridged amp is limited into low impedance loads.

Yes, start with speakers, yet at the same time keep in mind the type of amp you will pair with it. 
Try to audition and see what amp works well with each speaker.

I disagree with the approach of buying components for the short term, then upgrading them after a year.
  Buying used will get you more bang for the buck. The result is a higher-end component for your allotted budget.

Agree with others start with a speaker you like.

Agree with @inna in that I would start with speakers. Speaker choice will dictate the requisite type of amp that will mate with them properly. A satisfactory experience relies on understanding the codependent relationship that speakers/amps necessarily have with each other. A preamp must also pair with the amp in terms of its gain structure and ability to interface with the amp impedance wise in a copascetic(?) manner.
Everything else will be less finicky as regards to its "fitting in" with the aforementioned items.

I personally favor high sensitivity speakers as these typically open up more opportunities to experience the uniquely seductive amplifiers out there and they are perfectly at home with lower power (read less expensive). Many other would take a different path.

I've built at least 2 dozen systems from ground up & I've always started with the speaker system , a solid 80% if not 90% of your initial budget should be to purchase a set of " full range " floor standing speakers that go down to at least 30hz & 20hz js even better ,make sure you get speakers that your absolutely in love with the sound and the looks because with a big ass speaker system asthetics become very important in your home ,you already have a good quality " HIFI " preamplifier with your $700 Rotel ,keeping the Rotel and building the system with the Rotel as your preamp will allow you to spend your next money on amification ,while amplification is important you do not need to spend over $300 on a pair of professional amplifiers that will give you 500 watts of 8ohm low distortion power if you visit your local guitar center & buy a pair of Behringer A-500 amps ,they are roughly $150 each and when ran in bridged mono give out 500 watts @8 ohms which is enough power to drive any speaker system with a DB rating above 88 db which is a very inefficient speaker and the amps will drive them ,I've done it , for the digital sources I'd visit Emotiva dot com and buy a brand new Emotiva ERC-3 CD player at $400 or less and you'd have a good quality CD player ,I own an Emotiva ERC-2 CD and it sounds just as good as my $5,000 McIntosh CD player , I'd scroll down Emotivas products line and buy a pair of top quality 12 foot speaker wires with banana plug terminations for $120 ,then for power conditioning I'd buy the Emotiva EMX-2 line restoration and power filter unit at $159 for my amplifiers and the Emotiva EMX-6 power filter for my preamp and sources for another $159 , I use the EMX-2s on my 1200 watt McIntosh monoblocks and the EMX-6 on my McIntosh tube preamp and McIntosh CD/DVD player with excellent results , I'd stay with that system for at least a year before I upgraded anything ,then I'd upgrade the Rotel preamp with a used McIntosh C-2200 tube preamp of which I have owned 1 for a decade , the McIntosh C-2200 is a very unique preamp that is the best I've ever heard ,the preamp has the most effect on overall sound than any other components except for your speakers ,once you've upgraded your preamp to a McIntosh C-2200 tube preamp as long as you chose the speakers you love it only gets better & you may not need to spend big bucks on high end amplifiers and sources , if your dead set on upgrading to better amplification Emotiva made a unicorn when they made their XPR-1 1,000 watt @8 ohm Monoblocks you can pick up used for $3,000 fairly easy & they compete well with my $26,000 McIntosh monoblocks .

Speakers 1st ,amplification 2nd ,source 3rd,power conditioning & quality speaker wires and interconnects 4th , upgrade your preamp if you must 5th ,then upgrade your amps last if the 500 watt Behringers aren't driving your speakers well enough .

I would start with speakers. If you choose right you will enjoy them for a long time. Then power amps and speaker cables. This would make a speakers/power amps/speaker cables unit complete. After that - preamp to match the amp but also future phono stage and dac.
I would upgrade turntable/tonearm/cartridge last, this step is just as important as speakers. Tables/arms can last for decades.
But if you are going to buy used you will be limited by what's available at the moment, so it might be more chaotic and complicated. Ideally, you want to have the entire signal chain in your mind before proceeding. Still, speakers first, unless perhaps you want to use particular esoteric lower power tube amps and then match speakers to it.

I should mention the system will probably be used primarily for the turntable. After I source some HQ sound files, I can see streaming those frequently too. Maybe 50/50.
So I guess DAC would also be near the end of the list. And I'm also guessing either the TT or speakers would be the first thing to get upgraded. As to the order of the other pieces. . . . lol I'm still clueless.



Ps. Thank You, Al. I'll start looking for a good show to attend.

First, welcome. You have asked a question that will yield strongly held differing opinions. My recommendation, which I have given several times to others, is as follows: If possible, attend a large audio show. AXPONA is in Chicago in the spring and RMAF is in Denver in the fall. Both shows have lots of rooms that feature audio equipment you have probably never heard. Go into as many rooms as you can and spend your time listening to as many different systems as you can. Pay special attention to what equipment the manufacturers have paired together--often they have determined it is a synergistic setup that makes their equipment sound close to its best (this is not always 100% true--but it is fairly reliable). IMO, only after you have heard a lot of equipment will you be able to determine what system you are actually chasing. Then, IMO you should look for very good deals on the equipment you actually want. Don't buy it unless you are convinced you can't get it at a better price any time in the near future. This method should allow you to use discipline to wait for what you really want at a good price and your money will go farther to get a complete system that you aren't constantly feeling you need to upgrade. Otherwise, you may pay too much and not get as much as you otherwise would for the same amount of money.
Have fun--you are at a really fun part of the journey.
Regards
Al