So in the midst of covid I started this journey, then the price of lumber went up and the builders increased the price $20,000 the end date for this project moved and moved and moved again.

Should I add the other unit as a separate asset and take depreciation starting from 01/01/2020 - Date of Conversion (as I moved out in December 2019)?

A couple things: 1) With a job offer in hand you can actually use that income 90 days prior to the start date.

We have been tossing around the idea of purchasing a lot currently occupied by 3 mobile homes with the intention of holding them for a year or two and selling to build as many multifamily homes as we can fit. 

If you have better comps please provide the address, sale date, price closed and the appraisal.

As for your SFH lender, you'd need to check your specific loan terms, but technically most loans require you to live there for 1 year as your primary, so if your move has flexibility then I'd time the dates to align with the 1 year requirement.

You will need to find a good agent to walk through the property, and send you videos (One that you can trust)Get a solid inspection, identify contractors that will give you bids for any big-ticket items prior to you hitting contingency dates. 

I was blown away when I had to demo an old abandoned 600 SQ ft house on a mobile property I did

On the partnership rehab project, I was unable to get a solid bid on the rehab costs and a completion date.

The way we see it, if no one shows up, its our monthly date night with some wine!