On touch-sensitive amps
Keep in mind that some amps do the touch-sensitive thing better than others. It's a thing of beauty when all the bits of the amp (preamp, power amp, power supply, speaker) start to break up at about the same time. Look for a non-master volume amp with just a couple of gain stages and alnico-magnet speakers.
One thing that you're going to have to get used to is playing your leads with conviction. You're not going to get the singing leads that you'd expect from a cascading-gain lead amp (say, a Boogie Mark-series amp). Instead, you'll get a nice horn-like tone that responds well to nuances in your playing. Problem is, if you don't dig in on every note you'll have some weak-sounding notes in the middle of your solo.
Oh, and sustain comes from playing loud. The interaction between the guitar and the room sound helps keep the note going. Get into the zone (proper volume and postion), and you can pull out harmonic feedback at will with just a small change in your position relative to the amp.
There's a downside to all this, of course... Your lead sound comes from your technique, and not from settings on a few dials. It takes a while to develop your technique to the point where you can get the same consistency from a touch-sensitive amp that you got from a channel-switcher or a distortion pedal.