If you'll be racing in an area with trails thru the woods - or brushy areas, skip the baggy shorts & go with the tight bike shorts & jersey, or stray branches might just catch your clothes & unseat you! Curve, Inc. socks actually have a little padding in them, which makes them comfortable.
Padded shorts - for an XC race, a definate! The lycra blend wikking materials will keep you drier & cooler than straight lycra, and make sure you check the seams in the shorts - you don't want seams rubbing you in the wrong places when your out racing any distance. Generally, the more panels, the better construction a bike short will be - 6 or 8 is great. Bibs obviously don't have a waist band, so there's one less place for material to rub and irritate your skin. The pad should bave some anti-bacterial properties to it.
Darker colors will hold up better to washing, and, after a high temp race, will preserve more of your modesty - unless you're going for a heavy weight lycra, the lighter colors get kind of "see-through" when wet.
Try stuff on, and use what's comfortable - no matter what you get, unless you're hanging our with a bunch of other like-clad folks, you will look silly, so don't bother with a mirror!! Have fun!