Poodleshooter, I'll try to help...
1. What you were skimming off in question #1 was probably just lead oxide. Skimming off the dross is a good idea, but flux the metal well before you do skim. And yes, that is a big advantage of having a bottom pour pot. I have a Lee Production Pot that does the job well.
2. I have NO idea what the stuff was. Hopefully you didn't waste a lot of lead.
3. and 4. Temperature is important, but even more important when casting with alloys. I'd say just try to keep the metal at the temperature that works best for you. And, being a handloader, you can appreciate the importance of consistency.
It is possible to get a mold too hot, and when it happens to me I start getting frosty-looking bullets. That's my signal to slow down the pace a little...but then, I am casting with ferrous molds and casting alloy bullets. I wouldn't really know what to expect, casting pure lead bullets.
I don't think you'll damage the aluminum mold the way you're using it...in fact, you can dunk a corner of an aluminum mold directly into the metal to warm it more quickly and it won't hurt a thing.
If you're not fluxing your metal, you really should try it. I have taken to using Marvellux. It makes the lead oh-sooo-liquid and pourable. But you HAVE TO store the stuff correctly because it absorbs moisture, and we know what putting something containing moisture into molten lead can do!
As soon as you can, get your hands on the Lyman Cast Bullet Handbook. It's got everything you could ever want to know about alloys and casting!