1) I think all antenna connectors are pretty much universal in nature, so I wouldn't think you'd need any adapters. Even if you do though, a place like Radio Shack would probably have anything you needed.
2)I'm not sure what you mean by unused wires, but if they are by themselves with only a metal connector on the end, you can usually just tape them off individually so that there will be no possibility of electrical shorts in the future.
3)Your ground wire is one of the most important considerations for electrical circuitry. There are usually a number of components up in the dash that are bolted to the chassis. Just loosen one of those bolts, and fasten your ground wire to it with an appropriately sized wire connector. It's best to find bare metal, so if the part of the chassis that you want to bolt your ground wire to is painted, scrape the paint off to get a good metal to metal ground connection. Check continuity to ground at that point by setting a voltmeter to measure resistance, and measure between that point and the negative post on your battery. The needle should read zero ohms for a good ground connection.