Tube amplifier upgrade suggestions welcome.

Shawn, did you talk to the seller? Make an offer.

Last year a rebuilt RM-10 sold for $1700 and a recent unit sold for $1850.
https://www.hifishark.com/search?q=music+reference+rm-10

Well done. Best of luck.

The Lore specs from the website:

• 98dB 1W@1m
• 8 Ohm impedance
• 30Hz-30kHz frequency response

So, let's say in the real world these speakers have 94dB sensitivity. You won't need a powerful amp to drive these, especially in that small room. You may have a larger room someday so a tube amp with a minimum of 25wpc will do.
 
You could start by looking through the Audiogon classifieds for a lightly used amp. With a $2000 budget you'll find a larger selection if you go used.

Would you consider a used Raven Nighthawk integrated to be a better move than buying, say, the Parasound A23+ new and using my m2si as a preamp?  

A tube integrated would be a better way to go than using the MF as a preamp.
Raven builds highly regarded components, you should check user reviews of that amp.
I second adding  Quicksilver and Decware to your list.

Would you consider a used Raven Nighthawk integrated to be a better move than buying, say, the Parasound A23+ new and using my m2si as a preamp? This is kind of where I'm at decision-wise.  

My answer to this question was to stay all tubes and not  buy a Parasound.

Separates is a great way to go.
Use the m2si and find a used tube power amp. Quicksilver comes up for sale pretty often.

A rebuilt Dynaco by Will Vincent is a great amp. It has that classic tube sound.
https://www.audiogon.com/listings/lisa2a90-dynaco-un-limited-by-will-vincent-mondorf-caps-tube

A very highly regarded amp...
https://www.audiogon.com/listings/lisa8h87-music-reference-rm-10-mkii-tube

Of course you can keep this thread going. I'll second Jolida, aka Black Ice as a possible amp for you.

I recommend you message the seller of the RM-10 and make inquiries, he's the original owner.  Ask to see more pics. I expect this amp to sell quickly, they don't come up for sale very often.
http://www.ramlabs-musicreference.com/rm10mk2.html

Will Vincent regularly posts his restored Dynaco's.

shawn, the seller seems to have provided good CU pics of the amp. It’s very clean and he states it’s only 3 years old. Not much wear happens in that short amount of time except for tube life.

The questions I have are answered on the Music Reference website including:

Tube Complement:
2 Matched Pair 6BQ5/EL84;
2-12AX7

"Each unit is hand wired with point-to-point wiring."

EL84 is a very smooth, sweet sounding power tube. 12AX7’s are the input tubes and are widely used and not too expensive.
P to P wiring is preferred over using circuit boards.

I would ask how many hours are on the tubes, will they need replacing soon, is there a user manual, is there any transformer hum? (Some tube amps have a low-level hum that does not come through the speakers. It’s in their design). Ask if you can speak on the phone since it’s your first tube amp.
It’s a good price, probably because of the chip in the wood body. Definitely not a deal breaker.

I see your m2si has preamp outputs, so you're ok with just about any tube power amp.