OK... for you preamp needs, chalk up another BIG vote for the Sarno Classic Tube Preamp. Just beautiful tone in that thing.
As for your power amp needs... and keeping it small... a couple things:
- as already noted, a Mesa 20/20 could do the trick. Run it in stereo for 40 watts, or dial one side down for 20 watts. I haven't played much with this power amp, so can't say what the Mesa EL84s will mean for the tone, but I do remember that when I spoke with Brad Sarno to order my preamp, he liked that Mesa as a power amp for his box.
- Another trick: My FAVORITE tones to date... my current main setup... is running my Sarno preamp into the effects return of a very nice, simple 16 watt 6V6 powered combo. It's a Valve Train Trenton. The trenton is a wonderful little amp somewhere between a Deluxe and a Princeton. Bought it to have a small combo around. Had no plans to run the SMS preamp into it, but out of curiosity one day, I tried it (the Trenton is simple, but happens to have an effects loop, which makes this possible).
WOW!! It sounded amazing. That clear pure Sarno / Twin tone, but feeding into low wattage 6v6s, so it just wants to jump to life. Tubes really humming along at moderate volumes, and the strong signal from the Sarno really gets them singing. Not sure how much of this magic in the Valve Train specifally, or if you'd get similar great results with a different amp. Perhaps its the recipe of the Sarno pushing 6v6 tubes...?
All you need to try in a nice low-watt amp that has an effects loop. As for volume, this rig is plenty loud. I run it into a 2x12 cab, and it's been great in band practice, and also for good strong stage volume at a large venue (mic'd for front of house). And that's with a very loud drummer, and songs where I need plenty of good clean headroom.