Interim backup solution for Enterprise Manager

The only challenge may be getting communications established between your Enterprise Manager appliances and all of the other BIG-IP appliances in your enterprise. You'll need to ensure TCP 443 is open between EM and each device you want to manage.

I see no need to setup any kind of EM cluster/group. You can just configure each EM individually to gather statistics and collect archives from each BIG-IP appliance in your enterprise. This will provide you with multiple geographically separate locations to store configuration backups.

We use two EMs in our enterprise, and we have four different data centers with five BIG-IP appliances at each data center. Each EM takes configuration archives from every BIG-IP device we have on a daily basis. We have an isolated management network which we use for these backups so we don't impact production traffic. Your situation may be a bit different, but the overall concept is the same.

It sounds like what you want to do is easily achievable. Do you have any specific questions?