Your main concerns seem to be:
3. Data location/security
1 and 2. Google's chromebook/apps platform is completely free. You buy a chromebook (about $250) and a management license ($30) - and that's it. Your Microsoft products and their supporting management/backup software cost way more than that - I know - I bought them for years.
3. Backing up your data - google backs up your data to data centers all over the world and snapshots your data so you can go back in time - again for free. I've bought EMC and Dell SANs - even the cheap ones are very expensive.
4. Cloud/internet access. We have existing filtering systems in place, and our chromebooks work with those systems just like our old machines did. Google also goes one step further by giving you the tools in their management console to build web access policies. You can make web access as tight or as loose as you like. The really great thing is that these policies are applied directly to the machine. If a student takes a chromebook home, those policies are still enforced. This means that web filtering is no longer tied to your physical network located at the school.
The bottom line is that this is where computing is going. Just like it is usually not efficient to generate your own power and water, it will soon not be efficient to generate every IT system you use in house. Sure, lots of people will fight that trend, but efficiency always wins. It's going to be very hard to justify hundreds of thousands of dollars (if not millions) poured into your datacenters, when competing schools are doing similar things for free (or near free).