I did everything myself from cabinetry, drywall, flooring, windows, plumbing electrical, etc...

Maybe the foundation is slipping, the roof is needing full replacement, the plumbing backs up every time you are draining the tub and try to flush the toilet...  

However, if you're talking about flooring, tile, cabinetry, electrical, plumbing, etc... that will add up quickly. 2) Did you confirm the market rents in several ways/methods?

I can do all the basic things like lawn maintenance, snow removal, painting etc, and some electrical and plumbing.

Be attentive to damp ceilings or walls, which could indicate plumbing failures.Structural issues are critical to monitor.

Be aware of the costs as you'd need plumbing (water and sewer), electric and possibly a separate meter to the new unit.

Every time we have frustrating issues with it, like plumbing issues that involve the neighbors or the HOA, we hate it and want to get rid of it.

And you have a vacant unit to do the "proper" plumbing repair.If you offer them a rent concession, my money is on them going back to that well each time there is a problem, asking for yet another abatement. 

Many carriers have ceased offering new policies or will only accept properties in very nice condition with verifiable updates to the roof, electric, hvac, and plumbing.

I would say look at the big ticket items, roof, foundation, electric, plumbing, HVAC and assess from there if anything needs to be done