A '70 Satellite wagon I had was really transformed with up-sizing the front swaybar and adding a rear one.
The thing about brakes, besides fade, is that the better you buy, the deeper you can carry speed into a turn; also, braided lines help with feel.
As much wheel & tire as you can get in there, and given the car, yeah a "square" dimensional setup is most likely best. Power & gearing play into that a bit, and understeer/oversteer preference too. As far as Coopers, their Zeon RS dry tires have been great on my Mustang, and tires will be a consumable item on a RR.
I'd be inclined to put a proper oil pan on it for improved pickup & added capacity.
Stiffening the structure will make the car more predictable and separate flex from suspension response. Makes changes & tuning less confusing.
The seat & belt deal means at least 4 or 5 point, then bolstering, so the stock appearance thing is gonna suffer. Midpoint in that would be OEM-looking buckets with added bolstering, like what's available for early Camaros but not to my knowledge for Mopars, meaning a talk with a good upholsterer.