Per #1, that's already how it works. All you have to do is filter your games to whatever selection you want (for example, NES), and it will select only from that list for the random selection. If you want all games, just select all games first.
Per #3, you can adjust the volume control in LaunchBox. Probably not the cleanest solution, but it should work.
Per #4, there is a lot of custom stuff we could do there, yeah. I've considered that recently. It's probably a ways off, but I'm sure we'll get there eventually.