There are VA hospitals in charleston and in columbia, neither are convenient to Lake City I'm afraid. You may need to rethink if health care is a priority.
Social Security benefits taxed for federal purposes are not subject to tax in South Carolina. Code Section 12-6-1120(4). One of the reasons SC attracts so many retirees.
you may qualify for property tax exemptions when you buy, I'm sure there is a realtor out there with that info.
this is the official state info site.
SCIway.net - South Carolina Information Highway - SC lots of links.