A wader is necessary ? if so... what kind? the same is used for freshwater works?
Paul gave you some excellent advice to follow.
Regarding waders, here's the low down:
Since you are just starting out, using waders made for the freshwater angler will be okay...for now. Waders are one of the most important pieces of gear a surfcaster can own. If Surfcasting is something you end up really liking and want to expand on then I am going to suggest the following, actually recommend, you go with waders specifically made for the saltwater angler.
The fact is not all waders are made to withstand the harsh saltwater enviroment. I am not saying you need to spend hundreds of dollars, on the contrary, mid price waders that are made of breathable material, double taped seams and reinforced in the crotch, knees and backside are the way to go, especially if you eventually plan on climbing over some rocks or wading out to that outer sandbar.
Stay away from those cheap rubber waders as many people complain about them. Also, hip boot waders have no place in surfcasting.
Again, i give you these tips if you plan on expanding your horizons with surfcasting.
For now, while you experiment in the world of surf fishing, pick up a pair of Field and Streams from a place like Dick's sporting goods as they will serve you fine. I have a pair myself and still use them for the rivers and back bays.
As recommended by Paul, go looser so you can layer up if need be.
Good Luck out there and don't forget to post some reports this season. There is nothing like having the waves crashing down while feeling the salty spray against your face with the sun rising waiting for that fish of a lifetime to suck in your plug
add on: also, read this thread
http://njsaltwaterfisherman.com/forums/index.php?topic=20467.0