In general what I see as the crux of the sell/hold decision is opportunity cost. A

That's because the buyer/REI cost, as in what they are actually paying for the property, is only the cash that comes out of pocket. 

This has never impacted the ability to get a loan on the property, although it does increase insurance cost a bit as the insurance needs to account for the separate structure. 

Scott, I don't know if this would have helped you or not, but I can hire a hoe and operator for the same cost as renting the hoe from the rental yard.The machinery is better, the work gets done faster, and the operator is sure better.Yeah, I've occassionally broken something expensive while "saving" money by doing it myself.

The only gotcha I see is that it will cost a fair amount, like 3-5% average I think

I agree with @Trevor Ewen. a feasibility study (I think we're saying the same thing) is an EXTREMELY useful tool, despite the cost.  As

This will cost a few hundred bucks, on top of the few hundred bucks I've paid for the home inspection, and I have not even closed on the house yet so I don't really wanna be sinking too much money in while managing my risks.

These days I see tiny homes, pre-fab homes that dont cost as much as an ADU does.

I save money from my W2 and invest it in properties that cost as much as a pick up truck.

I think with wholesaling being so appealing to a new investor (because of the low entry cost) a lot of people dive in and with out the experience and either cannot comp the property correctly or get to ambitious in their asking price.