1) you generally want at least neoprene socks with adjustable fins in order to avoid blisters. full foot fins don't have that issue, but you then have the problem of cutting your feet if the shore is rocky.

2) can't freedive with the ffm as the volume you need to equalize is too large. there really isn't a solution to this other than getting certified for scuba and diving with a ffm.

3) you need to equalize if you freedive due to the increase in pressure. the most basic method is the valsalva where you pinch your nose and then force air into your eustachian tubes. if you get into freediving, most people end up using the frenzel or BTV method instead.

4) unfortunately, you need to try out a mask to make sure that it fits well, so buying online can be a crapshoot unless if you have tried the exact model on before.

the phantom aquatics mask+snorkel isn't bad though. add oceanic full foot fins and it is cheaper than the cressi palau set (which has a snorkel i hate)

https://www.amazon.com/Phantom-Aquatics-Velocity-Snorkeling-Titanium/dp/B00E1OBEN8

https://www.amazon.com/Oceanic-Viper-Full-Foot-Diving/dp/B00J28SPMG