100 ton to 500 ton osv

I’m.new here and have a few questions. I have a 100 ton and nothing else…except for my FCC and dp advanced . Been looking into the upgrade and was wondering at what point do I need to get pre approval from the coast guard to sit for the exams. Do I need all the ab, gmdss,stcw,radar, and whatever else they require first or do get the letter and then start taking classes. I been working offshore for about 13 years, so sea time is not a question .
Does anyone know if the sea school in mobile is any good for the pep class for 500 ton.

Well, dispatcher just called and its time to load some casing…looks like a great day for a boat ride. Y’all be safe!