"...difference between the small base and FL..." The SB die sizes a few thou smaller than an FL die. For a bolt action you don't need either, except for new brass or once fired out of another rifle. One or the other is required for a semi-auto, lever or pump action though.
"...like this to be precision..." You don't need the so-called 'match' or 'BR' dies to load match quality ammo. Regular dies will do just fine.
"...is RCBS ok?..." RCBS or Redding kit is far superior to Lee. The RCBS warrantee(Dillon too) is on the kit, not the buyer, forever. So if you were to buy used RCBS kit you still get the warrantee. They'll fix anything with a phone call or e-mail. Lee has a limited warrantee that does not cover used kit. Lee stuff breaks too.