Lol I expect an increase in overall cost.

Supply and demand is at an all time low.

It was said that the 2019 Tenant Protection Act has a negative effect on the number of rental units in some low-income cities (to the tune of 15%).

There are a lot of reasons people can have low scores and it doesn't mean that they would be bad tenants.

Again the below is just a best estimate - Do you guys think I'm factoring in 99% of the expected costs?

I have enough in savings to pay for it but I keep asking myself should i just sell it and get it off my plate and lose the low interest rate or bite the bullet and do a big rehab and continue renting it out.

Cost to replace.

But with this 42 units will sft cost will be lower than building 2 or 4 units and we need some guidance who has done this kind of construction/investment.I’m seeking expert advice from an experienced builder-investor in mixed-use developments.

If your focus is on speed, (e.g. because the seller dosn´t want to wait or give a financing contingency) you might consider a hard/private money loan, since they usually can close way faster than a conventional bank loan.

The other half is: excellent finished product design and management at a reasonable cost.