hello and welcome! Congratulations on the weight loss, cycling will definitely help with that.
I would suggest trying some different bike shops, some are definitely more helpful than others and will go out of their way to help. My local one is ok, but if I'd known how excellent the shop in the next one was I'd have gone there first.
I think there are a few threads on here from people who have had similar worries on setting out, they should come up on a search. I'll edit with links if I find some. Anyway, I think the verdict is that weight isn't a barrier to riding. Good luck!
Editing to add - nice post here. If you do a search on 300lbs or 250 or whatever you'll get lots of threads. I'm sure that more people with more specific experience will be along soon.