What are the major considerations I should be concerned about before enabling Einstein Activity Capture, particularly around data loss now that this has moved to Hyperforce and AWS?

I regret enabling EAC. The reporting is awful, you cannot get granular and you will have to create many custom reports and customize those fields and their lookups. Even then some reporting filters are "not supported" salesforce support doesn't really know much more than the surface help articles so you are kind of on your own. If you can hold off enabling EAC I would and wait for Salesforce to announce more supported filters and formulas