I know I'm lucky cause I don't have to worry about predators here in Hawaii...well, at least not where I live. We've got mongoose, but other than that only stray cats. I used plastic chicken wire on my run and haven't had any problems so far. As for your use of the chicken wire, I think people would say that the wire on the run might be a first line of defense against predators. If they can get through the wire, then they can't get to the coop door. If they can't get to the coop door, then they can't get to your chickens. Layers of defense.
As for the angle of the ramp, mine is a little steeper than 45 degrees. It didn't take them long to figure it out. They had no problem with the ramp. The strips of 1"x2" help a lot. I had my chickens out at about three weeks old and they could handle the ramp. I would think they chickens can handle a steep ramp. But, on the other hand you don't want to make it too difficult for the chickens to go into the coop. They may find it too difficult and just stay outside. I spent about a week of chasing the chickens and shoving them in the coop at night before they figured it out on their own. You don't want to have to do that forever, so I'd suggest making the coop/ramp comfortable and easily accessible so they want to go in there of their own accord.
As for the angle of the ramp, mine is a little steeper than 45 degrees. It didn't take them long to figure it out. They had no problem with the ramp. The strips of 1"x2" help a lot. I had my chickens out at about three weeks old and they could handle the ramp. I would think they chickens can handle a steep ramp. But, on the other hand you don't want to make it too difficult for the chickens to go into the coop. They may find it too difficult and just stay outside. I spent about a week of chasing the chickens and shoving them in the coop at night before they figured it out on their own. You don't want to have to do that forever, so I'd suggest making the coop/ramp comfortable and easily accessible so they want to go in there of their own accord.