#Do I need to buy anything else for this to work?

No external plugins or assets are required — the place runs as-is the moment you open it. The only thing you need to create yourself are the actual Robux dev products and gamepasses you want to sell (Speed packs, 2x Speed, Extra Slots, cosmetic purchases, …) through your own Creator Dashboard, then paste their ids into Config. Until you do that, those purchases simply tell the player "isn't on sale yet" instead of erroring — see Configuration Checklist.