One main thing I’m questioning is if I should upgrade kitchen with new appliance and hvac system.

Those are upgrade calls, where nothing is wrong but tenant wants to improve something.

I have firsthand experience inheriting tenants in properties we purchase from bad landlords (those who don't fix broken windows, respond to maintenance calls, etc).

I've looked at a number of properties lately where part of the value add is to improve amenities while also upgrading interior units. 

If it's tile, does it look like any don't line up properly, are broken or missing? 

They get the same jobs every time we upgrade a unit.

You may find that even if competing houses aren't offering granite or other upgrades it may pay to install it so that your property will sell faster and closer to list price than your competitors.

All the setup incl. permits were included with the exception of the plumbing, sewer, electrical upgrade and HVAC reconnect.

They say that the pipe had only been broken for 2-3 hours before my friends arrived.

Rental income is good and vacancy rates are really low.I would also say with a little work on your end you upgrade the units and raise rents especially since a 4 unit is not subject to ETPA .