Looking for advice on an all-purpose campaign ship

I'm planning to build a ship that can beat the campaign on its own (starting on Easy, since I'm bad at the game).

I have a few questions:

• How large should the ship be?
• How much armor is generally recommended, and where should I prioritize it?
• What weapons work best for a reliable all-round campaign ship?
• What defensive systems should I include? For example, anti-missile lasers, CIWS, decoys, LAMS, etc.

I'm looking for a balanced design that can handle most campaign encounters without relying on support ships. Any general building tips or common mistakes to avoid would also be appreciated.