As others have posted, camo at an indoor site is irrelevant due to the close ranges so wear what you like.
As for other kit, full face protection is highly recommended, exactly what is up to how comfortable you are but remember ppe is far cheaper than dental treatment. Also I'd add a torch or tac light to your kit for those darker areas and a bag of pyros and/or BFGs (assuming the site allows them)
Gunwise I recommend something short (obviously). I found a couple of GBB pistols worked best as they allowed me to be more agile at tight corners and the faster trigger response meant I could get shots off quicker.