This is more or less what we use at my current place (100s of engineers). We haven't run into any dramatic issues at this scale. Our architecture is arcanist/p

This is more or less what we use at my current place (100s of engineers). We haven't run into any dramatic issues at this scale. Our architecture is arcanist/phab over git --> stash (git) --> custom build server that's basically identical to gitlab --> artifactory. we use pants, but we made that choice before bazel was a thing. Bazel is probably the most "scalable" solution, but it isn't always the most intuitive/developer-friendly. It's worth exploring the alternatives (biggest ones imo are pants, buck) to see what you like the most. They're all pretty similar, but Bazel has some hard-to-replicate bells and whistles that mean it'll probably be the eventual winner.