Congrats on your new trailer!
1) Yes- you should purchase a WD hitch with sway control. This TT can be more than 5,000lbs loaded so you will need it.
Do you know what WD hitch with sway that they are looking to sell you? My advice is to stick with Equal-i-zer or Reese. I've heard good things about Blue-Ox. There are others but I'm not really familiar with them.
As a price comparison, you can get the Equal-i-zer from RVW
for $439 including free shipping.
2) Remember that Forest River will sell you a 2nd year for $150 within 10-days of purchase. This is a true extended warranty.
Everything else bought through the dealer is not a warranty as in an extended manufacturer's warranty, but is instead a service contract. Be careful about those as some are OK and some are not worth the paper they are written on.
Make sure to understand the contract's legalese, what it covers, what it doesn't and if other service centers will honor it. You can search on this board and find other posts about this, too.