Cashier's check OR cash is OK.
Bill of sale (Include VIN, you are selling "as-is", etc)
They should show up with license plates? Definitely don't let them take it without it, unless of course they bring a tow truck/trailer
Check with the R/DMV as to how to do a sale/transfer of title. Every state has different infuriating means to do this, and you may need to get something notarized to make it official.