If you're going opto, may as well go with a proper opto isolator to avoid joining ground planes through the RX; I've had signal issues when joining up non opto isolated high power ESCs.

Also, the HSOF packages ideally need thermal vias and to be heatsunk through the board. You can heatsink the case but it's not as efficient. Without a heatsink you'll likely get about 160A cont from 4 of those FETs, so to get to 300A you'll need to dump a lot of heat.