Output IO Buff is too large; DDR3

No, there won't be anything DDR3 related. Altera has their own altmemphy for DDR3, which has constraints(although deciphering the scripts that write the constraints is painful), so they don't have constraints for do-it-yourselfers. (You say it has to be simple, but DDR3 just isn't simple, and that's why I would recommend using the Altera core). If you want to do your own, you'll want to start with being able to do source-synchronous double-data rate interfaces(note I don't put DDR, since people always assume it's the memory interface), as that's an integral part of transmitting and receiving data in relationship to a clock. But for DDR3, it's just a start. Look at the documentation on altera.com, and I just put a document I put together on the topic up...