You know as well as I do correctly configuring DNS takes all of 5 minutes
Try openchange its a protocol complete re-implementation of exchange. If you're looking for more of a "drop in" windows server ad/exchange/av/fileshares etc look at zentyal.
Gotta remember the overheads of exchange are immense which would free up a load of resource both compute and storage/ram for you to use else where. Barking up the windows tree is costing you serious time/money especially when you have better linux based skills available to you. Perhaps time to stop thinking like a big enterprise and start thinking like a 2/3 man band.
Just suggestions but I've just gone through exactly the same migrations with 2 of my clients both are 400+ members of staff and the cost savings have been insane let alone the administration time/costs on an ongoing basis. I'd much prefer you had solid ancillary services and so could spend more time working on the actual game code baseI don't have loads of time available to me but could probably help out with a couple of hours a week if you need help with smaller bits to allow you to focus on the important stuff.