1) You would need to compile the coin from its github source, this is technically not so hard but requires a small learning process, it could also easily outsourced by anyone. After that put the wallet on our server and we have made a script that easily adds the markets and necessary variables everywhere. Although we made it as easy as possible, this is still something that I strongly advice a developer does however.
2) Our coin wallets are divided over 3 separated servers, high value coins like BTC and LTC reside on one, while brand-new untested coins reside on another. Only the trading engine can access these wallet servers, and only the front-end server can access the trading engine.
We keep over 90% of funds in cold storage, for BTC we use Armory for that. We have a fraud-checker in place that will scan every withdrawal request for abnormalities and block the payout for manual processing if need be. Basically we have covered every trick in the book to maximize our user funds safety.
3) The platform is written on Node.js using Express. A developer with sufficient knowledge of javascript would be necessary to develop new features.