Questions on Upgrade of CMS 7.5 SP1

I am upgrading my CMS 7.1 to 7.5 SP1 . Planning to configure CEM. Already read through the Implementation Guide and Cloud-enabled Management White paper. Need advice on the following 

1. Is it possible to use my existing reverse proxy as Internet gateway ?

2. Is upgrade going to affect my daily backup of Database ?

3. Also have configured NAC in my network . will the upgrade be affected by NAC  ?