[YjSe2GMQ]

Disclaimer: I don't know anything about managing a team, this advice is more for a solo developer or a developer joining a team.

#2 is what I use. After one/two hundred tiny commits (even if it's sometimes just fixing grammar in comments) you'll feel more at home. And because they're small you can achieve that within a few weeks.

This requires any way of telling that things still work. Sometimes you'll be able to do that because the transformation is an identity given the language definition, but for other cases I'd encourage #7. Having someone more senior (with respect to the codebase) review changes helps (this is what I mostly used), but I understand you don't have that option.