If you can get a spot in the park and don't mind dry camping, then do it. It will save you time and money. You are going to have a blast in Yosemite. It's, IMHO, one of the easiest NP's to see thanks to a wonderful bus system and a centrally located valley with attractions very close to one another compared to other parks. Snow would be rare in October in the Valley at 4000 feet of elevation but in the high country it is possible at 8000ft but you won't likely be up there in October if there is snow unless you visit the ski resort.
If you must stay outside the park, the Mariposa KOA is nice but I prefer Indian Flat in El Portal. It is the closest RV park to the entrance of Yosemite.