Hi, Gambler,
Dollar Tree is a double edged store. LOL.
You can get good deals on canned veggies, many canned meats (tuna, chicken, vienna sausages, etc.) and snacks like chips and cookies.
The bad news is that most of that is not actually healthy for you longterm (as you said). A LOT of sodium in most things when you look. BUT, you can find things like fruit cups, applesauce, the veggies, cereal and peanut butter. The sizes are smaller usually than same brands in grocery stores so you'll want to compare to know which things are a good deal.
The other problem I have with Dollar Tree (and I shop it often) is that it is easy to pile up a lot of "it's only a dollar" until you suddenly have 25 of them. LOL
Keep us posted. Sounds like you are spending the time to learn all you can before making the leap.