Jazzie, you are pretty mixed up on this stuff. I suggest you take the time to either read up on it here:http://luckymojo.com/graveyarddirt.html
or pay a rootworker such as myself for a half-hour session of magical coaching so that someone can explain it to you. There is a lot more to say, but here are quick answers to your questions:
1) No, usually three coins, not one. Dimes are favoured, but pennies and quarters are common, as are 9 coins. These are family traditions and they vary from family to family.
2) No. In Afro-Caribbean tradition, but not in typical Southern conjure, you may make two payments, one at the gate, one at the grave. Most Americans do not do this.
3) No, you need not bury the offering. It is quite common in the South to lay the coins on the headstone. These are family traditions and they vary from family to family.
4) Whiskey is optional, coins more common, burial more common than not, but absolutely not demanded. These are family traditions and they vary from family to family.
5) Yes, that's pretty typical of those who live in small towns; they'll especially go where their people are buried.
6) You may be having a problem with English. To LOOK BACK is not the same as to GO BACK. To LOOK BACK means to glance back over your shoulder as you leave. The fact that going back to visit your Grandfather again after working with him before seems "counterintuitive" to you signifies that you are not of this culture and have yet to meet and learn from people who are actual practitioners.