Who Gives A Fish Forums

I'm getting frustrated with the conflicting advice. Thought I was making progress, then someone comes along and says the opposite. Starting to think I'll just stick with what I know - freshwater.

Running eight freshwater tanks, plus 30 years under my belt. Thinking of dipping my toes into marines, possibly converting a 2 or 4 footer. Not looking to go full-on reef, just a few fish and maybe some shrimps. What kit would I need for a basic setup? Any advice on this and some guidance on fish ...