Help building first tube system.

For tubes, Atmasphere- MA-60 with an MP-3 or UV-1.
Vandersteen VLR's
Rega Apollo CD player
Bluesound Node
Ayre Codex DAC.
If you buy used, you should have enough for good AQ cables and maybe a Vandy Sub 3. Though if you splurge on the AQ William Tell speaker cables, you probably won't need a sub.- And, I heard em.
You could save a bit if you went SS and just got a Belles Aria integrated amp. (That's what was connected to the above mentioned speakers/ DAC/Streamer when I heard those William Tell's connected.
Truly a WTF moment.
Bob

How tall are the ceilings? $20 K deserves some travel to a metro area with a few dealers to get an idea on speakers FIRST.

Naim Uniti Core music server $3,000, Audio Mirror DAC $2,500, Manley Jumbo Shrimp preamp $4,600, ATC SCM20ASL Pro mk2 $5,500.  Balance for ICs, PCs, stands, etc.  I believe the Naim doubles as a network player.  Speakers are active, so no amp needed.

This system would be terrifyingly good.  Obviously, everything here is at full retail.  Best of luck building your dream.

That system leaves $4600 for 4 power cords, 4 interconnects, and 1 pr speaker cables. That's an average of only $500 each, with nothing left over for Cones or even any room treatment. The only thing terrifying is the lack of awareness of the importance of everything left out.

For a first system in a small room you might consider something like a Decaware amp and Omega speakers or other high efficiency speaker. For sources just do a little research on CD players, streamers, dacs as there are a lot of them. I use a fairly inexpensive NAD CD player connected to a Benchmark DAC3B and a Node2i connected to the same. Ignore the nonsense about magic mats, fuses, contact pastes and other dubious tweaks and stick to the main components. Once you're  done that reasearch room treatments  and speaker positioning and how it can offer you best sound improvement.  You also don’t need to spend a fortune on wires some research there will go a long way too. Good luck.