Additionally, I don't have the time to sift through all the legal jargon and pinpoint where they’ve breached the contract, so it's worth having a lawyer review it in my situation.

Since you have no contract, there is nothing that says you do not have to pay if you are not satisfied, and your spreadsheet would seem to indicate you owe him the money.Similarly, since you paid him for previous work on the spreadsheet, and the spreadsheet shows you owe him for additional work, your argument is not very strong.

Given Covid related material and supply shortages, should I plan additional buffer time around my contractor's estimates. 

In addition to my real estate expertise, I’ve spent years building and collaborating with property management companies.

Your mentor has needs; try to meet them and develop a mutually beneficial relationship.A mentor can benefit your growth, but it's not as simple as one post on a forum full of strangers.

Here are a few additional insights that might help as you transition into multifamily:First, when scoping out deals, relationships are key.

I got a very good price on the building (about $25k per door), but it was a ton of work as in addition to tenant issues, there was TONS of physical distress (foundation repairs, sewer line and water line repairs, electrical upgrades, new roof, and apartment renovations needed for all units). 

The longer the maturity rate of the bond, the higher the yield is to compensate an investor for the additional risk they are taking on with a longer dated bond.Stocks that pay divideneds....insurance companies have a lower yield than telecom stocks as a reflection that telecoms are higher risk than insurance companies.In the efficient market hypothesis, if markets are efficient then the yields should be reflective of the risk.

I'm not 100% committed either way between the income benefits of multifamily vs. the reduced headaches of SFH tenants.

Additionally, we will see the unemployment rate tick up another .5%, to 4.9+ maybe even over 5%.