Hi and welcome!
If you have access to an indoor pool, swimming is one of the best low-impact exercises you can do - because it's cardio and resistance training all in one and is very easy on the joints.
To get involved on the forum - just dive in. I'm still new myself, but it seems like the more threads you visit and comment on, the more feedback you can give and get and the more enmeshed you get in the group. So far this is a great group of gals!
My high weight was 383 in May, but today I'm at 339 - so I'm right there with you!