cross-app relationships and performance

If you cause apps to be in a single process, then you deny yourself to have multiple threads,  running on multiple virtual servers. 

But performance will depend on how many concurrent users and the complexity and amount of data in the apps. 

If you expect to have a lot of users and a lot  of apps (12 is a lot) then if you avoid binding them together in one process try hard. My preference is sync tables. If you can possible live with the hourly refresh cycle.