If you want others to contribute, you should market / describe it as a betting app that does those things, and not an assassination market. With that out of the way, you could host it anywhere, like Github, and run Git over Tor. As for the language and framework, that seems fine. A core part of this app would be interfacing with bitcoind, and you can do that in most popular languages, including Python. https://en.bitcoin.it/wiki/API_reference_%28JSON-RPC%29