The RP will take place in the Capital Wasteland and will be around the middle of the Fallout 3 storyline. So the Enclave is all over the Capital Wasteland now and they are in control of Project Purity. The Lone Wanderer is not in the RP. The Brotherhood are currently trying to gain access to Vault 87 but are failing and are thinking about hiring a group of Waste Landers to get in through Little Lamplight as they cannot get in. There will be limits on the factions you can join, because well I do not want there to be a whole crap load of factions as that can get complicated.
But yes, the actual Plot Line is based off of Fallout 3, I thought that would actually be pretty fun because it does not have to end that way it did in Fallout 3. So please post any thoughts on this, thank you and goodbye!