To DYI or not to DYI?

LOL, you mean is there a first time?. You know your skills, look over the solder joints and see if you can do them.  I had quite a few first time...

I removed all the old boards on a Pass 2 pre amp. Built all the new boards, rebuilt the PS, and changed all the front switches and pots.

IT worked perfect. Took my time, checked my work and was one great sounding little preamp with or without tone control.. Tape loop.. and a phono section if I remember.. That was a lot of soldering.

Regards

I was one of the first to purchase the Marantz BA312 PE01 Upgrade on Ebay and I did do the upgrade myself on my 2275 and that took me at least 3 hours. But this looks a little more intense. But, I'll think I will dive in.

Swapping/upgrading caps is an excellent DIY. Get a good soldering station, a couple different kinds of solder, rosin, and learn to do it right. Learn a little something about how things are made. While you're at it get some fO.q tape and apply it to the caps and the PC boards. Find some good diodes if they're not part of the kit and upgrade those as well. Just that one part, diodes, you will be surprised at the improvement in liquidity, depth and detail. 

Cap and diode swaps like this were my first DIY/mod. In my case I just made a list of caps and bought much better ones. The potential problem with this is better caps tend to be larger. It can be hard to fit them in. This should not be a problem with a kit. The tradeoff is not getting as good caps as you otherwise might. 

But you can go round and round forever down the rabbit hole of which cap for what sound. When in reality any of them will be worth the time and effort. 

I mentioned different kinds of solder. Most guys will tell you what to use. Whatever it is, will have its own sonic signature. Using a couple different types of solder will avoid the risk of doing something that imparts a particular sort of sound. A bit obsessive but its the kind of thing done by high end amp makers like Raven.

Thank you for the your input. It will helps me decide on to do with my Marantz amp.
I was looking at this kit on eBay for $185  - which I believe it's on the high-end but might pretty thorough on the layout.
Marantz 1150 1150D 1152DC amplifier rebuild restoration service kit
https://www.ebay.com/itm/164155407528?ViewItem=&item=164155407528

Then there is this kit out of Europe that's maybe a little less but I might be on my own on where the parts are to go.
https://www.audio-high-store.com/product/marantz-1152dc-upgrade-kit-audio-capacitors/

Another thing. Some kit don't include the power caps like this reasonable $50 kit from Reverb.com  Is replacing the power caps necessary?
https://reverb.com/item/27104330-marantz-1152dc-restoration-kit-caps-trimmers-transistors-quality-pa...

Usually the power caps are the first ones that people talk about replacing.

If you’re going to crack it open, I’d go all the way. You would immediately start to plan a PS cap replacement the second you plugged it in and decided the first mod was successful, no??

Got it. I didn't know if they are a problematic caps or it's just a matter of upgrading. Thanks.

Is replacing the power caps necessary?

Yes.

One helpful tip: When replacing electrolytic capacitors, be careful to observe polarity of the parts you remove and those you install! failure to do so will result in a damaged part- the cap will draw power and heat up rather quickly. Once they've heated up they are not reliable. So make sure you get this bit right!!