Firstly, good idea camping OOC for your first event. IC is more conveniant in a lot of ways, but it’s extra hassle and you don’t need that when faced with the rather overwhelming first jump into Anvil 
Any sort of tent is fine in the OOC area. Bell tents, campavans, geodesic bright neon ones… whatever.
As for size, it rather depends. I’ve heard some pairs of folks do fine with a 3m bell, but it depends on how much equipment you bring. Camp beds are good, as you can stack things beneath them. Storage boxes are good, as you can empty them and then use them as seats (IC with a bit of set dressing).
Hum, generic camping at Empire advice only, as I don’t use a bell…
Bring some black bin liners. Useful for keeping muddy boots on, dry kit in, muddy kit in, etc.
LED lanterns are very useful.
If you’re after a wood burning stove, I would ensure you have it ventilated (I’ve seen some tents with built in chimneys) and still be damn careful. Fire and Carbon monoxide poisoning are a risk.
I have a camping gaz stove (one of the low ones, acts like a 1 ring gas burner) that I use in my tent. Carefully, checking the temperature of canvas above and near it. Works well, and allows hot drinks in the morning
There may also be useful info in these threads: