We use separate repos and it works out well. It's nice having separate Git histories that pertain to different areas of the codebase. Our workflow covers all t

We use separate repos and it works out well. It's nice having separate Git histories that pertain to different areas of the codebase. Our workflow covers all the potential problems you named (eg. scripts to keep everything up to date, tests that get run at build or push time after everything is already checked out from the individual repos, etc.). We've been running this way for over a year with literally zero issues.