Can any experienced players give some tips on the best accessories? How about accessories for other party members that request them?

Bracelets and charms are the best for Rush IMO (HP and AP boosts).

As for other leaders just give them anything they ask for, especially when Pagus and Blocter ask for their Remnant ones.

Soldiers will (eventually) clone the best bracelets and charms leaders (but not Rush) have for themselves, giving your unit good HP and AP boosts.