If you don’t afraid of ugly representation (which actually can be fixed with CSS) you can use fossil-scm which is used (and written by the same authors) by SQLite. It is just a single executable file. It’s comes not only as SCM, but has embedded WiKi, ticketing, email notification…

can I host a mail server on my home server and use cloudflare tunnel.

No. IPs of cloud flare are blocked on most email servers and you really need port 25 be opened. Also residential IPs are in PBL lists, which also used on email servers to get rid of army infected PC. If you going to get intermediate proxy, choose them carefully due to a lot of cheap (or with bad reputation) hostings are rejected (or has much more spam score) too