I also provide fridge/stove/microwave which I am ok replacing/repairing as needed.  

Water heaters, furnace, plumbing leaks, replacing a roof, replacing the main water line, tree trimming, microwave replacement, etc. $20-25K would be awesome but you can likely get by depending on condition for $10-15K. 

You'll do this for everything in the home that requires replacement: interior paint (4 years), flooring (12 years if you use 12 mil LVP), roof (20 years), hot water heater (10 years), oven, washer, dryer, garbage disposal, microwave and so on. 

Another option is installing a microwave with a vent above the range, but most built-in microwave vents are recirculating and may not adequately filter the air.I'm seeking advice on the best course of action for ventilation in the kitchen.

Other easy ways to exceed expectations might include microwave hoods, dishwashers, adding a shed, including basic mini-blinds, etc.

., microwave, diswasher washer dryer$10000 plus the GFI and power outlets $3007) input new light fixtures$3000 painting of the whole house$4100Clean up $ 400temporary toilet $500temp power?

So if a microwave has a useful life of 7 years, I say it’s closer to 5 years in a rental.

They pretty much haven't been in the place for the last 2 months (water was shutoff in December last year), there is still food in the fridge, the microwave is growing its own forest, trash everywhere, food everywhere, the walls/carpet are just... nasty, and I won't even describe the bathrooms...

I don’t think anyone fixes microwaves/dishwashers you replace them.

This can be attached as well, in which case it's essentially a duplex but the ADU is smaller, may only have a kitchenette (sink, fridge, microwave), and isn't zoned as a plex.