Don't buy Renthal sprockets unless you want to save a few ounces (if that.) Just get the cheap steel sprockets, I garuntee they will last at least 4 times as long, and 1/4 the price! But hey if you're into racing and want so save a quarter pound or so go for it....or ya could just go on a diet for a day or two. ;)
Also, they use an 18" rim for a reason, so you can run taller sidewalls and prevent pinch flats in the trails/dez. 19" rims are nice for MX (doesn't feel quite as squishy in the corners) but they are no good for woods, rocks, roots, etc. Michelin doesn't make starcross tires for 18" rims (or at least I have never seen any) but their other tires are pretty damn good, M12 front and S12 rear is a killer combo. Or Dunlop D756's are great...but tires is a whole other can of worms.
Congrats on the new ride! ;)