This really isn't the right forum for this, but I'll be a lax moderator and indulge it, since I'm going to slant my answer a little tech.
If you're looking for saturated tones at low volumes, smaller amps can be a great way to go. There are some things to be aware of, though. First, the wattage will go a lot further than you'd imagine. A little 5 watt Champ through the stock 8 inch speaker can easily exceed 100 dB. There are two reasons that people need more than 20 watts for club use: clean headroom, and to keep up with loud bandmates (usually hard hitting drummers). Either of these concerns can come up in studio situations, but for typical one-instrument-at-a-time home studio use, the later is certainly irrelevant.
There are certain tonalities that high powered amp topologies deliver that might not be as easily realized in lower powered amps. That being said, there are possible gains in terms of signal integrity due to fewer components in the chain, and also lower powered amps are often designed in such away that they will exhibit compression characteristics often favored for lead playing.
BTW, I am speaking in the context of tube amps. Low powered solid state amps IME tend not to have any particular benefit relative to their tube counterparts.
Particular online resources you might check out for DIY include the AX-84 project, which has several low powered projects associated with it, www.18watt.org (I think), which is a group focused on DIY builds based on the 18 watt Marshall tube amps, and www.firebottle.com/ampage for more general discussion.