Don't assume you need a type rating to act a a copilot. It may be a requirement, it may not. Also don't worry about inexperience. I do think you ought to instruct for 500 hours or so. It can be done on a part time basis while you're a part time copilot, surely. And being solo in thick cloud will do a lot for your confidence. If you get really comfortable flying airways and approaches at 1.5 nm per minute, it's a small adjustment to got to 3 nm per minute on an approach, which is about all you do in a jet below, say, 3,000 AGL.