Do the magnets impact the GoPro?

We have done over a year of testing with various different GoPro versions and have had no impact to the GoPro operations.  The compass and GPS functionality still work correctly.

Do the magnets affect the SD cards?

Unlike spinning hard drives and magnetic media of the past modern SD cards are not impacted by magnetic fields.  Here is a statement by SanDisk one of the larger SD card manufacturers https://kb.sandisk.com/app/answers/detail/a_id/4687/~/sandisk-cards-environmental-tolerance-%28waterproof%2C-temperature%2C-magnetic-and