..have seen some finished rifles, and the quality is high...so suspect his tubes are top notch.
I'd have to ask him...call or email...as I'm not sure what "extra" needs there might be.
For DIY use, a pressure rated tube, with all the holes and slots in the right place, and new end cap would be the start point. Could do the valve work, assembly, adjusting, and tuning.
Don't see a .25 as a good choice in a "do everything" PCP. Really, the only good reason for a .25 is power...if you don't need the power, can certainly use a .177 or .22. Kept that one simple, and once it got to +50 foot pounds, I quit playing with it. I certainly do not need a 50 foot pound .25 to plink with, shoot pest birds with, or hunt tree squirrels with. The only real use I have is to occasinally take out a big critter...so it really covers about 5% of my hunting.