sand & paint bottom

[hardboiled]

People i started sanding the bottom paint with a 220grit sand!? is this ok?

Now after i finish removing all, which paint i need to buy? How many coats do i need to add and do i have to use a primer or something like a gelcoat barrier and where do buy these stuff?

Please if someone can give me exact detail of each product i need to buy or if there is an easy guide online let me know. thanks alot