1. Depending on your UPS, most large suppliers actually have configurations that will allow fairly seamless connections to vCenter where you can give them options to control the servers in the event of power outages. Of course, you'll want to tune them properly so things don't shut down completely on power blips. Having the UPS control the host will in turn have the host gracefully shut down VMs.
2. You can enable SSH for ESXi either through the web interface or directly through the console, see: VMware Knowledge Base
1. Check the UPS vendors recommendations for VMware vSphere.
2. You shouldn't give your users ssh access. On ESXi ssh is meant for troubleshooting only. You can set granular permissions in vCenter and users can access it either through web interfaces (html5 or flash) or command line tools (PowerCLI, Data Center CLI, pyviomi, etc).