Hi guys, sounds great Linaru
I'm interested in making custom mobs, doodads and puzzles although I've only made one complex map so far, it's all good programming fun.
I think the best way for a team to get going is to open source the design projects in hosted source code revision control. One way is using free github repos, there's a small learning curve with using GIT, but once you've got it set up the developer leaders can only allow contributions once checked thoroughly. The major benefit, which NekoBaron addresses, is that people will lose interest so additions to scripts/doodas/items/etc can be arbitrary in size using Git and new campaigns can easily branch off or (merge into) a set of decent custom game files (all be it this adds to download speed in lobby, but repos are 1GB limit anyway)
I might make some custom mobs and tiles I'm working on available this way, to give an example of how a Hammerwatch custom map team could work, thanks.