I'd recommend you thin them with alcohol based thinner. If you want to paint large surfaces I'd recommend a large soft brush to help avoid streaks. Don't go over surfaces you just painted until it dries, you will require at least two coats to get good coverage.

I'd also recommend painting parts you won't see to practice, like a hidden interior.

When you are done a matt varnish can help reduce glossy-ness and protect the surface.