If you started on FM server now its sad time my friend. It will be closed in two weeks, where it was supposed to open a new season in 2 days. This wont happen. (In the previous 3 seasons was amazing experience.)
You can still enjoy the next two weeks on Frostmourne and you dont need to switch as you will have the opportunity to transfer your toon to ICC realm. Unfortunately the realm is heavily overgeared, (go to Dala , every 2nd plater has Shadowmourne) so you will have hard time to find any group in the beginning. Good luck.