Edit* Forgot to say, nice bike. Congrats!
Edit#2* I can say ass? Really? Thought that was censored. Ass! ass! ass!
Seats are totally a personal choice, everyone's ass is different. Grips too.
I'd suggest, before spending money on a new seat and grips, ride what you have for a while and see if you get used to it. Get some padded cycling shorts and gloves first, and put some ride time in, your ass will toughen up.
After that, go to your local bike shop and ask to try out some seats. Many shops will have demo seats to try before you buy.
For gloves, I personally prefer full fingers with little to no padding on the palm. Something like this: http://www.pricepoint.com/deta...s.htm You could find something similar at your LBS where you can try them on before you buy.
Helmets are a personal thing too, since head shapes vary, but I've always liked the way Giro helmets fit. If you don't like the normal style bike helmet, look for a skate style lid instead, something like this:
http://www.pricepoint.com/deta...9.htm These will be hotter, and probably less comfortable, but may look better to you. MX helmets (full face) are entirely too hot and heavy for regular trail riding. Again, try them on at your LBS, then buy one there.
Once you get familiar with what you like/don't like, in clothing, parts and accessories, you can venture online to shop. But just starting out, the support you get from a real bike shop is invaluable.
Modified by amish_matt at 6:11 AM 3-26-2009