If I wanted to do the headers later.., could I put the cat back on now and then when I do the headers put the H or X pipe in?
Or do I have to do do the H or X in at the same time as the Cat backs?

 

That is a good plan. The "breakpoint" in your exhaust system is the junction bewtween the Catback and the forward parts (Headers & H-pipe). You can do catback now, and then later do the headers + H (or X). However, you more or less must do the Headers + H-pipe at the same time.