Git is still bad at handling binary files so I would only use Git for the source code. The requirement for locked file notifications is important and Git doesn’t really have this feature so you can easily end up losing work because it can’t be merged.
Perforce works great in UE4 (also for source code) for any size of team but the free version has some strict limitations and it is not cheap.
So if you don’t want to use Perforce then at least pick an SVN solution like TortoiseSVN, and optionally use Git for the source code.