If the company is rotten it's time to find a replacement.

Heaters and filters last a long time but eventually need replacing.  

My area it is $6 sf to replace. 2500sf*$6 sf= $15000/10 year life span/12 months in a year= $125 per month for 1 item in a capex budget.

When we lived in Michigan the city we lived in had strict inspections that had to be conducted for a fee to redo burned homes.Realize that while you can encapsulate some of the burned wood to eliminate the smell, the heat does change the structure of the wood and may dictate replacement - again factor that into your offer. 

As you replace them, be sure to point out how easily sound travels between units, stress the quiet hours, etc.

When you do a cash out refinance, you are basically paying off the existing mortgage on your home and replacing it with a bigger mortgage (up to 80% of the value of your home.)

We purchased this property off the MLS in 2019 and replaced the roof and renovated the vacant unit of an inherited tenant who's lease expired.

You also don't have to worry about a tenant bring in their own and the damage that may cause and if the units break, the tenant has to replace it. 

New kitchen, bathroom, added an owner's suite to the home, new plumbing and electrical, the HVAC worked but I had to replace the coil and duct, refinished floors.

If the property is already rented and I’m just keeping it as Is with tenants in place and it’s got older systems in place and I figure some stuff is going to be needing replacement shortly I’ll use 8% and I’ll also try to have some cash reserves in place.