How close are you to Fort Stewart and when will you be 18? You can PM me if you don't want to respond in this thread. I have some work there very soon and will last several months. I will find out more tomorrow.
Work is slow compared to 2 years ago but if willing to travel it can be found although it helps to have connections.
The certifications you need depend on what field you want to pursue. Pipe, structural, boiler tubes, shop work, field work, etc.
It also depends on what processes you want to use predominately. SMAW, GTAW, GMAW, FCAW are the most common. Generally, pipe welding is the most lucrative but not always. The more you learn the easier to find work. Any company that wants to employ you will be responsible to test/certify you. You will need to be good enough to pass the test that the company requires you to take for them. Usually a couple of plate test (groove) for structural welding and a 6G pipe test for pipe welding but there are so many combinations and variables it's impossible to give THE test that's best for you. I suggest that you pick a process and craft to start out with and achieve that goal. That is only the beginning. You can add to that at the pace that you are able to and the opportunities that you have.
Sounds like you are on the right track. Drug free, responsible, eager to learn, on a great forum seeking advice from some of the best in the bidness. Not me, the others.