As mentioned, if you're not fully vaccinated you won't be able to enter France at all. After January 15, you need to be fully vaccinated and have a booster to be able to get the health pass that allows you to enter museums, dine at restaurants, etc. IIRC, you're not considered fully vaccinated until 14 days after your final shot, and you're not considered boosted until 14 days after you receive the booster.

In other words, if you want the health pass, you will probably need to be fully vaccinated and boosted by January 29. I'm not sure that's even possible if you haven't even started the vaccination process yet. Up to now, I haven't heard anything about needing a booster to enter France, so if you start right away (or get the 1-shot Johnson & Johnson vaccine) and nothing changes in the meantime, you can still get here, you just won't be able to go to bars, restaurants, or museums.