What kind of screws for crawl space vents?
Doesn't look like there is anything special here.. The vent itself is not sealed, so not sure why you would need to seal the edges with caulk, but it won't hurt if you do. 

I don't really see any reason any special screws are needed if it's just wood around the outside. I would just probably put in some #8, 1 1/4" to 2" screws.