Putting a 21" on the front wont change the ride much at all. it raises the front of the bike 1 1/2" so the center of gravity will change ever so slightly, you should be able to adjust to it within 5 minutes of riding.
The wind buffeting wont change at all.
The factory fender is made to fit an 18. Unless you know how to stretch a fender the right way, or have access to someone who does, you will need a new fender.
Hotvic.com offers a wheel, tire & fender package that includes a fender, painted to match, using factory paint. it also comes with the necessary spacers and mounting hardware.
Regarding a 23" wheel. You would need to add raked trees to get it to ride right. Hotvic.com also offers this as a package, as well as one for a 26" wheel.
2008 Vision Street
Custom paint; tinted turn signals; Lloydz cams, timing gear, PCIII; Hot Vic 26" Windmill wheel, billet wedges, tips, pegs & covers; Focal IC-130 5.25" speakers, Arc Audio KS 125.2 BX2 AMP; Hot Tails custom seat...
2012 High Ball
Custom exhaust; high performance air filter; Hot Vic sissy bar, lowered 1.5" rear, .5" front; Witchdoctor 2" peg extensions & pegs, Hot Tails custom seat & passenger pad...