Yep the role doesnt need to sit on its own box. It can share the proxy role.
It depends on how many VM's you're replicating, and how much data. We started at 100GB each site and grew as we saw fit.
Yes, you can change the job. if it doesnt work for you, change the job to not use WAN acceleration.
Quick caveat. You need to build up the WAN acceleration cache, so you might not see any efficiencies until the cache has been populated.