Yes, I already told you to use 5GHz if possible. I don't know what kind of main router you have, so I don't know if it has 5GHz or not. I was just explaining why it would be better to use 5GHz for your bridge router.

For your other devices, it really depends on how far they are from the main router and what kind of interference there is (walls, etc). All else being equal, the 2.4GHz will reach farther than the 5GHz will.