Welcome! I'm on the other side of Columbia from you, so my answers should be considered guidelines. You may have other options in Sumter.
1) SC CCW instructor
Not sure of who in Sumter teaches, but
www.scfirearms.org should help. Locally, Paul Peters or DR. Katz give excellent classes. Be advised though, you need to get familiar with SC's CWP laws as there are some twists and turns for the unwary.
2) FFL for transfers & on site retail purchases
Several vendors here in Columbia. Palmetto State Armory has their retail outlet here and there is a Sportsmans Warehouse on I-26, Piney Grove road intersection. Shooter's Choice is a decent gunstore and has an indoor range. May want to check with Bud's gunshop for a FFL in Sumter. Mkdrgn (THR member) is in Lexington, but we are a 45 minute (+) drive for you.
3) Full service gunsmith for routine repairs
If you can catch him, Phil at Innovative Arms in Elgin is about it. We have a severe lack of gunsmiths in the area.
4) Indoor pistol / rifle range
Shooter's Choice in West Columbia is the closest to you. Some rifles can be fired there, not sure as to what. The range is very restrictive. Decent for accuracy work, not much for practical shooting.
5) Outdoor rifle range (100 yards+)
There are several. One near Charleston (may be closer, not sure), Mid Carolina Rifle Club in South Congaree and Mid Carolina Gun Club near Orangeburg.