The estimated value came from Redfin (which is more than likely high) but even if you call it 680 those numbers make sense.

How do I get a realistic estimate of what this new bill would be?

A written estimate from 'Sinkhole Titan", from November 2021 to pin the home, was provided to me by the owner and that cost was worked into my numbers.

Relatively new to the home buying process, but actively searching for my first investment property.My question is around estimating the renovation cost during the purchasing process.

I know the pipes would probably cost around 10k to replace haven’t gotten an estimate on the trees yet.

Do get multiple estimates though.   

Please let me know what you guys think about the rent estimates and the rehab costs (being optimistic with just painting and installing new carpeting in the bedrooms) as well as any other aspects you have input on.

Income approach is better for you.This is fine and dandy for a layman's estimate, but you should have a professional appraisal before listing an $8 million property.

Know your numbers and make sure it will cash flow after all expenses and estimated income.

Order appraisal, estimate repairs.