The wire you are talking about SHOULD be the power antenna wire, assuming it was installed right in the first place. I have no idea why that switch would need grounded. Assuming that wire actually is the power antenna, it only has power when the stereo is on.
Any time you have bare wires, you should at least tape them up, especially if you don't know what they are.
As for roll starting, so long as your alternator is working and there isn't a break in the electrical system, it shouldn't be a problem. You can use reverse no problem, while going forward first or second is fine. Just make sure the key is in the ON position, I forgot to turn it once, and that was an annoying mistake to make.