Jarco will happen first then Starco.
It's basic plot building tropestry, first ya make them go through hell to let them in heaven. Jarco will be a gruling three or five episode arc that will start happy as fuck for them then quickly plummet to the depths of bullshit for both of them. After nearly killing archother and Star going fucking insane as shit marco and jackie will break up peacfully and the next episode will be like nothing ever happened. Then Starco finally happens in the final four episodes.
Screen shot this for when I'm right so you can post it and be like "i was there man! I was there when anon predicated some obvious crap!"
Im going to sleep.