Replacement crankset for MegaExo BB 24mm on 8 speed bike
is there anything special I need to consider for the 8 speed?

Yes, you specifically need an 8 speed crank.
8, 9, 10 etc speed group sets use progressively narrower chains, and the cranks have narrower chainring spacing to suit.
Many people seem to think you can get away with one speed difference and there are special shims available that adjust chainring spacing but it’s easier to just get a explicitly compatible crank.
Be aware that FSA MegaExo road (68mm shell) is dimensionally the same as Shimano Hollowtech II road, so you can fit a Shimano crank. Personally if I were upgrading to a Shimano crank I’d upgrade the bottom bracket to a Shimano unit also.