Well for Starters you ain't the only one who loves Ventus he is an awesome character especially w/ his ability to use alot of speed attacks
for grinding levels for all 3 characters I found this strategy pretty easy (May be time consuming but worth it) before you begin make sure you have 4 Mega Flares and the 2 EXP Abilities Walker and Chance (EXP Walker gives your characters the ability to gain EXP for every 1 step you take while EXP Chance gives you more EXP when you have Critical HP) also make sure to take off any prize pick up abilities as well as Treasure Magnet you don't want to get the green orbs to heal you next go to Radiant Garden and head to the area before the area where you fought Trinity Armor let the Unversed Drain your HP to Critical then head in the area to where you fought the Trinity Armor move over to the center then head to the edge from where you entered the center and cast Mega Flare till there is no enemies left then exit and rinse and repeat and with walker equipped as you are heading outside your still getting EXP thanks to EXP Walkers ability