a) volume levelling is best done with Spider Edit and it takes time, and maybe a good db meter. That's all there seems to be to it. There's no shortcuts about it, as the effects take on different personalities depending pre/post amp positions. There is one fine tuning trick that can be done with the boost button, by raising and lowering boost db settings, you can increase volume without drastically affecting tone, as long as the rest of your pre-set levels are fairly close.
b) Tube screamer is a fairly decent sustain effect built in, but dialing in sustain is another trial and error deals. There are a few effects that will bring sustain, but a lot of them just bring distortion and/or compression.
c) Pre-sets aren't set across the board each time they are adjusted. the same effect will have two different settings depending on the channel/file that it's saved to. Each time the pre-set channel is selected, the pre-sets will come up the way they were last saved, whether on or off, however they were set, they were saved.
d) I haven't figured this one out yet, but I'm thinking it has to do with heat and computer circuitry. There is a huge heat sink on the back of the amp head, and I'm guessing it's probably insufficient to the task of dissipating heat, especially if the drummer drops his jacket behind my amp. The simple fix is to throw his jacket into the toilet and see how that works...but for now, since it's winter, I'm going to look around the forums to see if there's other heat related issues called out, and I've bought a small, cheap fan to set on the floor behind the amp to supplement air flow around the heat sink...we'll see. If the drummer puts his jacket on my fan, he'll get a really stern whaddafuq and then I'll make that trip to the bathroom. That sounds fair to me.
It's been a month, and not a bad one really. I've still got the peavy sitting in the corner crying, and it looks as though I have one more issue to solve before it goes on e-bay or off to the music store.