I don't know anything about Veteran benefits. Hopefully someone esle will chime in with advice on who to go to to make sure you are getting what you should and where you can get help with PTSD. Using GI benefits to pay down credit cards doesn't seem like something you can do. Even if you can
Take a look at the investment order:
https://forum.mrmoneymustache.com/investor-alley/investment-order/Based on this good general guidance consider:
1) Paying off your high interest credit card debt with your investments. This is a guaranteed 10+ percent return on your investment.
2) Negotiating a payment plan you can stick to with your dentist and see if you can get low or no interest (they should prefer that to not getting paid)
3) The IRS likely already has you on some sort of mandatory payment plan
4) Are the VA debts in addition to these? What kind of interest rate, payment plan are you on? We need to know this to provide sensible advice.
5) increasing your emergency fund as you suggested or higher.
Make a budget for you $1500 income that avoids going hungry. A single person should be able to live on 18K a year without worry about food or shelter.
1) That means you need a new place to live. You cannot spend 900 on rent out of a 1500 income. Get a place with roommates. Move somewhere cheaper.
2) Buy cheap staples in big bags from the grocery store. You may not want to live on potatoes, rice, beans, onions, and lentils, but it beats the hell out of being hungry. If you buy food in 20 pounds sacks you should be able to not go hungry on even a $100 a month. Then supplement with eggs, milk, and the veggies on the best sale that week. My favorite discount grocer is Aldi, but any place should be able to sell you 20 pound sacks of staples for <30 cents a pound.
3) After a place to live and meals, prioritize your mental health. It sounds like the VA already recognizes that you have a disability from your time in the service. Please make sure you are getting the help you need. If medical costs are related to your military disability, shouldn't these be paid for? Someone with experience, please help.
4) Transportation? I can't tell what your current situation is with a minimum of $100 per month spend. If you are already going without a car, great. If not, can you? Can you at least minimize car use, while not working?