Predator proofing open air coop

[aart]

This is a hasp......and I'd put 2 on the nest access.
Caribineer to 'lock'.... chain so lock isn't lost.

 

[perkolator]

Ooh I need to add tethers to my carabiners now! Dang kids keep moving them

I agree on the lock change. The hasp and carabiner is probably one of the most secure setups and quite simple.
I think the wood gaps are ok, you could also add a strip of wood to fill if you were concerned. The roofline holes I resolved on mine by cutting hardware cloth and stapling to inside edge so a rat/mouse/small bird couldn’t pass through. They also make commercially made flashing that is made for corrugated panels, but that’s something else to spend money on

 

[Llillyfnp]

These are the latches we have over food door and nest boxes

 

[Windrider]

Everyone else has you covered on the other issues, but I've got a perspective from also having an open air coop.

At first, my coop had a solid roof and only one solid wall - it was built against a cinder block wall. While the raccoons couldn't even get their little hands in anywhere, they would climb on the hardware cloth at night and terrorize the roosting chickens. I modified just the roosting area to have three solid sides. That made a nice sheltered area while still keeping the majority of the coop open.

 

[Chuckie chicken]

This is a hasp......and I'd put 2 on the nest access.
Caribineer to 'lock'.... chain so lock isn't lost.
View attachment 2293525

*Immediately goes to shop and makes tether for carabiner.*