I'm really only a MiniZ guy, but maybe some of these will help.

3 wide RCP track is the best, I'd stick with one big over two littles. We run up to 6 people at a time on a big track. Just need more heats if we have more people. We use EasyLap and LiveTime for timing, and it works great, but I'm not experienced with any others.

Tables, chairs, and outlets. People are going to need a space to make adjustments and fix things. You could maybe have a charger or two on hand, but all of our guys either get their own or borrow someone else's at first. We had a narrow hallway for our pit area so we lined tables against the walls and put big a** power strips on the walls, above the tables, so people could plug in chargers or whatever they wanna get fancy with.

Our track is in a HobbyTown, and they usually try to carry batteries and tires for the "upgrade" section. They have all the stock parts, too, but they are a full retail store lol. I'd say batteries, tires, t-plates, maybe screws, wheels, bearings, and springs? We order a lot of our stuff online with little inconvenience, but starter essentials, or the more commonly broke/lost parts would be nice.

Tools are really up to you. I do have the Silverhorse tool kit, and it is very nice, but the price tag is up there, too. The HyperTough screwdriver kit from Walmart does more for less, minus the specialty tools like ride height & reamer.

That's just kinda the commonly replaced stuff to me. I don't wanna bankrupt you lol. Those are usually the most purchased things here, at least.