I’ve compiled a bunch of links of the multi-repo vs mono-repo choice. It’s been a hot topic of debate at work.
Advantages of monorepos (2015) - Dan Luu on why a bunch of large companies use monorepos and a bit on the tooling for them.
Repo style wars - monorepo vs multirepo (2017) - covers a bit of the pros and cons of each method. Also has a list of monorepo tools.
Monorepos in git (2015) - a piece from Atlassian. Decidedly against the idea, mostly because the tool won’t scale. Though in 3 years, things could have changed in git-land.
Monorepos in the wild (2017) - again pros and cons, examples of Google and Facebook and a bunch of tooling. A good read.