How can I create a 2d vampire survivors-like hell game?

I’d like to create a 2D, reverse bullet-hell type of game in pixel art. I plan to make it a 4 person co-op, which includes different classes (such as Knight, and Mage) all with their own unique abilities and upgrades to choose from. Characters later on would be able to branch out to additional classes (so the player can opt into being a mage knight for instance). This allows me to easily expand on the game with each new class. Additionally, I’ll take a stab at making a couple of levels players can choose from, each with at least a few different enemy types.