Can we do a self check-in if go early before 8am? Any code for a gate?

No you can't the gate doesn't open until 8 a.m. if you're already in the park you can get in and out but if you're just going in for the first time you have to wait and check in with them

Access is open and if no one is at the gate at the entrance, you pay at the exit of the visit..good day