If you decrease your x dimension lets say by one inch, and use a five blade will it make the boat ill handling and also will it suffer in the rough seas.

That probably depends a lot on what your x dimension was to start with.

I Raised Mine 2.5 Inches And Its Now A 70 Mph Boat......if Your Gonna Raise It Go A Little More Than You Planned ....if You Have A Bravo It's Easy To Lower It With Drive Spacers .....really Hard To Go Up If You Want More