A warm welcome to you.
As said, ... backing is a good idea 'cause ya might hook something else.
7-8wt is what I use for sea trout on the slaat. Not because of the BIG trout, ... but because of wind and bigger flies.
You can also think of getting a WF or shooting taper.
If you are into it, and depending on the fishing, a shooting head can be handy.
Last choice,(for me) ... but maybe an idea to look into ... a nice spey rod.
Where exactly do you fish to be chasing after sea trout ??
------------------
Christopher Chin, Jonquiere Quebec
[url=http://flyanglersonline.com/travel/quebec06fishin/:8516d]2006 FishIn Ste-Marguerite River[/url:8516d]
[url=http://pages.videotron.com/fcch/:8516d]Fishing the Ste-Marguerite[/url:8516d]