I was a GM for years before I joined this site, on a few different roleplays, but I don't think I'd want to try starting a group RP here. It seems like group RPs here have a much higher chance of dying than on my previous forum. Maybe it's just because there's more roleplayers here or something. Anyway, when I did GM I preferred people who could be active, even if they may not be as good at writing. It's detrimental to a group RP to have people that are barely there and only posts once in a while compared to the rest of the group. It often means people are left waiting for them to post which might end up slowing the whole RP down, even having it die. I often mentioned what kind of activity I wanted out of players, and yet somehow always got that one that didn't bother sticking to it. I liked to encourage collaborations too. 

As a roleplayer my standards have gotten higher and higher over the years it seems. I don't like GMing anymore, because there's always that one person who manages to make it a chore for me rather than fun. I used to do a lot of group RPs too, but I find just following someone else's lead gets boring very fast. I like to have some creative control over what I write. It doesn't really help that some of the groups I've joined lately have had people who feel the need to make their characters the strongest no matter what, players who just mimick what I do or has a bad GM that's plain rude. I find 1x1 RPs the best when they're actually good, but those are not easy to find for me either. I do get more creative control in a 1x1 RP though, and with a good partner it's still as fun as other forms of RPs used to be for me.