As for vehicles, anything pre-1980. I do anticipate an EMP event and I don't trust all the electronic wizardry in modern vehicles anyways. Too expensive to repair.
Retreat-wise. 20 acres of arable land with a shallow water table under it. Preferably within driving distance a town of 10,000 residents or so. Those number will be enough to defend against maurauders. Have some perimeter defense around it to keep people from driving up to or even into your house. Fences with gates that are not for decorative purposes. Defensive landscaping techniques.
Gun wise, pretty much anything will work as long as you have more ammunition than your potential adversaries. Long rang capability is good. If you can shoot them, but they can't shoot you, you win. Pistols are a must as the home invasion robbery scenario will be all to common.