places to buy parts
the music electronics forum and Weber's kitbuilding forums are resources to learn about what you're doing. www.tone-lizard.com
is another source to look at, especially the page where he goes through a typical amp circuit and explains what's going on and what happens when you change things. Download some of the instructions for some of the amp kits that are available online, like the ones for Tube Depot's tweed deluxe kit.
some suggested reading would be Dave Hunters's Guitar Amplifier Handbook and Aspen Pittman's The Tube Amp Book. Another if you can find it is Kevin O'Conners The Ultimate Tone series, particularly the third volume.
As far as what is gonna give you the tone you desire, I'd suggest going to a well stocked store and trying the tube amps out, especially the ones that are reissues of the classic circuits. the '59 Bassman LTD, DRRI, TRRI, A Marshall model 1987 or 1959 Plexi reissue, Vox AC15 and AC30 are the kinds of circuits I'm talking about. If you think you want a modern two or three channel switching amp, I'd suggest you just buy one. Or else build a couple of the simpler amps first before trying something as complicated as a Mesa clone or similar.
Hope this helps you out, but watch out, because amp building can become it's own form of addiction.