I tuned my guitar to D modal. Thats DADGAD.

But now the strings are a bit too loose. Any way to counteract this?
Try pulling REALLY hard on both sides of the fret board. This will stretch it out and make the strings fit better.

Please don't do that.
go 10's they should suit it. btw are you just dropping the 2 E strings to D and the B string to an A. what gauge string your using now?