Er okay, please remember that you still should not install TS on a domain controller! I would recommend just getting another server and getting the SBS premium add-on for TS (not expensive and it is basically just 2008 R2 standard). What do you mean by cheaper? They already have SBS! Exchange is great, what would you replace it with? To be honest it sounds like you have no idea what you're doing. I suggest hiring an IT company that can provide real support and setup Microsoft products correctly.