When you refinance at the new ARV, the lender will want an appraisal done, and they'll pass the cost for this on to you. 

They need to see purchase contracts, rehab estimates, comps & CMA's (they'll still want to get an appraisal though), your LLC docs(if you use one), Trust info (if you use one), etc.

However, when the appraiser went to look at the home, she found out that there were tenants in there and now the underwriter wants them out BY CLOSING!

Then we had to wait with bated breath for our appraisal.

For option three I'm looking to find a mentor, real estate agent and/or appraiser that can help me understand the underlying value and marketability of my lot for multifamily as a comparison to adding an ADU. 

@Layla Sewell I'm not sure if it'll work in South Carolina, but in Florida you can go to the county property appraiser's website for the county the home will be in and find a 'tax estimator' tool. 

Maintaining cash flow post refinance is important and I imagine that those monthly payments/taxes may go up once we appraise and refinance at the higher value.

Bank loaned me $$ for the remodel then got it appraised and they released the sfh.

Usually just an appraisal fee and it won't mess with your existing mortgage.  

All you care about is the appraisal.