@Ethan GarrettThe amount of your win is inversely proportional to the combined wins of the seller and buyer.

If you separated them shortly after purchase I would probably just allocate your total purchase basis in proportion to the FMV of the individual two plats on the date of separation.

Factors tied to the escalation in values would includeDecrease in listing availability Increase in buyer demand (at least in proportion to listing availability)Interest rates being blissfully lowBuilders being businesses that needed to hedge their bets early in the COVID mania and reduced new construction paceCurrently commodities needed for construction are significantly elevated over pre-COVID levelsThe GOV is passing out cash like candyAll of these forces and a few others combine to create an up-and-to-the-right kind of housing market. 

We are paid directly in proportion to the problem we are solving what i learned.

Assuming your CPA says it makes sense to do the cost segregation, the big ticket items will be asphalt, sidewalks, flooring, landscaping, site work for drainage and compaction of the area under driveways, appliances, wall coverings like drapes, fences, etc. 

I own dozens of homes with knob and tube , not a huge deal , people blow things out of proportion on here .

If proportional billing is common / legal in your area I'd say definitely look into it.

Make sure the house layout is good for room renting (rooms are on the larger side, max 2 people per bathroom, parking on street/driveway is not too compact for the neighborhood, ...)Be clear in the lease about potential problem areas... 

It would be ok to fill the pool with dirt only if it was properly compacted as it was filled.

I can't speak to the legal risk as mentioned by @Travis Moe, but frankly, I find that others are blowing other risks out of proportion.