➡️ What are the estimated costs of upgrades for the semi-upgraded and fully upgraded units?

You have to weigh the cost payments of each and see, which is better or lower for you!

They may be easy and relatively inexpensive to add sub-meters for the secondary unit, or they may be significantly intertwined, making it much more costly to separate.

Is it just time and experience, knowing what costs what or is there a better way? 

It's harder to finance good properties right now for obvious reasons, and if you go NNN or DST then you need to be very clear about the costs (upfront and ongoing) that might eat at your returns. 

CPAs seem to be very expensive costing thousands of dollars!

If the ADU actually costs you $500K, it's barely worth it in terms of cashflow.

Keep in mind the cost of doing business is that Vesta has to take a broad array of liens from Mr.

Used the 3% realtor commission as a credit towards my closing costs.

It's the cost of doing business.