MRR, it's all that matters in the first stages. MRR = Growth = Customers.
- CAC is not worth it, and you could be spending money to early
- CR is something you should track but only important if people truly hate your product(hope you're adding more than the people leaving.)
- LTV is only useful if you have data to back it up. In Year 1/2 you're still measuring this and guessing.
I would track
- Customers talked to each week
- How many converted
- MRR Weekly
To me that's all that matters. If you want to track other stuff, then those would be secondary metrics.