A couple of thoughts and ideas from the peanut gallery over here.
First thing I'd do in your spot is to find a community band to be a part of - skip community orchestra for the moment IMO. Right now you are looking to regain ability and improve, and orchestral music can be a bit tedious for that - you'll have more opportunity in a concert band. Surroud yourself in a section with people better than you - nothing will help you improve faster than having a real gig or concert on the horizon and trying to bring yourself up to the level of the folks around you.
Second, I'm going to go against the grain and say to look into getting a new horn if you have the coin for it. Believe me when I say that there is nothing like the buzz of a new instrument that makes you want to go get it out and put in some time. When my son was starting to show some real promise as a guitar player, I put a real Gibson Les Paul Standard ($2000+ guitar at the time) in his hands. I think that kid would have slept with that guitar if he could have, and because he loved the guitar so much and was putting in so much time, the amount of improvement he made in the following year was exponential.
Third - mouthpiece. Find something middle of the road in terms of size that's comfortable and stick with that. As you get more time in and you start to rebuild chops you won't feel the need to go to a different mouthpiece unless you get to a point where you are trying to specialize. In my case, I do a lot of playing on a Schilke 14A4, but that's only because the bulk of what I play is rock and roll horn lines where I need the added brightness to the sound. I've never gained any range with a mouthpiece - it has made it easier, but it didn't give me anything I didn't already have. When I'm not working on the rock and roll stuff, and on the occasion I have a more classically oriented gig, I play on a straight Schilke 14 - middle of the road in terms of diameter and depth, and gives me the kind of sound I need for it.
That's all I've got. Keep us posted, and welcome to the forum!