That's a big component of the overall cash-flow picture, so it's important to know where it comes from.On the other hand, looking closer at these numbers, I see the ARV is $25,000 less than the project cost. 

You can only 1031 exchange long term rental "Investment Properties" and property that is used for business "Owner Occupied".However, since this is hypothetical, if the IRS allowed you to 1031 flip properties, then you would pay taxes at your capital gains rate (once you sold the last property and didn't replace it) on all the gain from all the properties and 25% on any depreciation taken during the the hold periods.

Looking for a contractor that can replace bathroom subfloor ASAP.

For example, after refinancing you find a lender with better rate, does this happen and do people replace the original mortgage with a newer one?

Maybe they are just trying to get everything replaced by complaining so that they never have to pay anything out of pocket. 

I'm not a flipper by any means so I don't know the ins and outs of foundation and framework if it needs to replaced every now and then.

Also it appears you need to have your evaporator coil replaced due to door missing and large gap at the base of coil box. 

Seller has agreed to replace the roof for this price. $44.74/sqrft.Our plan is to renovate the units as they become available

My area it is $6 sf to replace with a moderate lvp.

The seller needed to replace the siding so buyers could get a secondary market loan on it.