we are having a similar setup except we have more than 300 dedicated developers, we have exactly what you described several revision we need to deliver to different customers.
We have divided it so we have an initial ref like refs/heads/platformX.Y/ then we build on that
So depending on what you need to do you checkout platformX.Y/develop and start working from that point on a feature branch and you merge back to develop when you are done.
This works for us and we can follow the nvie model.
on top of everything we are merging all these platformX.Y branch to our main develop branch so errors corrected on those branches are released in to the latest software as well.