Panniers & what else?

I'm new to bike packing so am trying to work out a decent setup for a 5 day trip I'm looking to do soon. I have a carbon gravel bike without any mounts, so my options are a bit limited.

I already have a tailfin pannier rack with two ortlieb bags, a top tube bag and a small seat pack. My first question is whether this is likely to be enough capacity for five days (not camping) trip, and secondly whether I need something like a bar bag at the front to balance out the panniers and stop the bike being too "rear heavy"?