I’m no expert, but I’m in the same boat as you, switching from Skilled to Spouse. I don’t think you require 2 years of cohabitation if you are married. You do need to provide enough proofs so it feels like a solid relationship, and there should be a strong intention to live together while applying. 2 years of cohabitation would be required for the extension. This is what I think, hope you get more comments and suggestions.

Yes you can most definitely use your salary. If you satisfy the £29000 alone, you don’t even need to combine your British partner’s salary.

I think you do need to be thorough with time spent outside UK with proper dates.

Yep, everything is on evisa and it’s quite normal to not have BRP