It all depend on how many of you are going and on how big the vehicle. IMO only 3 peolpe are able to fit into a normal saloon with gear. We are 4 so we're renting a minivan.
Everything wil fit alright
You will buy a bike rack for ther bikes, so they don't take up any space. Water, if packed correctly doesn't use as much space as you'd think it does.
Suitcases can be a problem.
Pack light. Don't use all of your baggabe allowance when flying in.
Also buy some of the stuff this side of the atlantic on ebay. Sometimes it is cheaper than in US shops.
I recomend at least buying your tents here and bringind them over. That way you can test them out first.
The worst thin you could do is buy a brand new tent before the event and never put it up once. It could be missing a pole or anything.
I think this year I will bring my shade structure with me as well as my second bag.
It is small enough not to be charged extra.
You can get dust goggles and stuff here online if you want or in US. The advantage of getting stuff here is it gives you plenty of time to make it beautiful