Answers

here is a link to a good article on How to get squirrels out of an attic.

http://www.aaanimalcontrol.com/professional-trapper/squirrels-attic.htm

We have a client that recently dealt with a similar situation, but it was a racoon. They installed a one-way door, made from galvanized mesh, over the hole. Once the varment was out, the clean-up and repairs could be made. There are liquids that be applied that will keep them away once everything is sealed up.

On the squirrel removal, best to call a trapper or get a trap. 

That area agains the home can be covered with some heavy guage counter flashing and sealed up prior to that with some fast setting mortar. 

Wood is the best attic stairs.