If you were comparing RE/MAX Broker A to RE/MAX Broker B, then I would say it probably doesn't matter.

Run your own airbnb comps and see how your rates, pics, and amenities, compare to them.

Obviously I want to keep my costs low but still want to spring for amenities that would give me a competitive edge compared to other rentals.

We recommend you get management contracts from several PMCs and compare the services they cover and, more importantly, what they each DO NOT cover.

Comparing these metrics before and after the addition helps identify if the amenity is driving more business.Increased Rates: Some amenities allow you to justify higher nightly rates.

With some more math, you’ll see that the extra amount in dollars is not that much compared to the total amount of interest paid.

Compare that to the performance of a new property (with that equity unlocked but also with a different interest rate as @Katie Ripp said).

It would be based on the scope of work of the renovation that you're doing comparing for values in its as is condition and values after rehab 

I find that depending on the market $300-500/mo are fairly normal and if compared to what you would pay with a single family home on some utilities, maintenance, and management, it's a good deal.

Compare other rentals with a similar size, location and bedroom count to get an estimate of what the rent would be while you're living there.