Section 121 exclusion rental to new construction primary home

[Pablo Madrid]

I am buying a house next month with a rental on it primarily for the land value (urban Houston). There is a month to month tenant on the property which I will keep to offset holding costs while I design the home and I close on my bank loan for new construction. The hold time will likely be 3-4 months until the new construction loan closes. At that point I'll kick out tenant, tear down/move the house and build new construction which I will move into about 12 months later. I plan to live in the house 2-3 years and sell for a tax free profit from a section 121 exclusion since it will be my primary house.

I have multiple rent homes some generating a tax profit by now so writing off expenses on the 3-4 month hold cost at this rented house is worth something to me. Appraiser said structure is worth $5k so my depreciation is negligible in this timespan. Haven't found this situation online yet as most people don't tear down a rental but this is in a HCOL urban neighborhood where new construction comps are high and I got a good deal on the lot.

My questions are:

1) Assuming the timeline above, 4 months rental, 12 months personal home construction, 24 months primary residence then sale for 121 exclusion, how does the non-exclusion-eligible taxable portion prorate? 4/(4+12+24) = %10 of profit to be Long Term gains taxed? Or because the original structure is worth basically nothing and I'm building new is 100% of the profit eligible for 121 exclusion since I will live there 2+ yrs? Does the construction period count as part of my 2 yr test for 121 exclusion?

2) I have other SFH rentals I just Schedule E and that's it. So do the rental losses get to offset other Sch E income when I tear down and build new? (assuming I Schedule E this property for the 3-4 months it's a rental)

3) is this all too much headache and is the $800 bucks a month income not worth the blip/headache to my Schedule E portfolio even though taxes, interest etc could be a write off for those months?

Thanks!