You have a roster to do Act 5, but I'd say you might as well finish exploring Act 4 first. The long paths in Act 4 can help a little w gold, and if you throw an XP boost on you can get your summoner level up as well (to 60). I think you'll get some basic iso and 4* champ w act 4 rewards too, rank up materials. That said, I'm not sure if you're Uncollected, if not do that first then go back to finish Act 4.