That was a substantial discount compared to my friends who were paying 2k+.

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

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.

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.

A carryover basis would be a huge downside though compared to a basis step-up if held by parents until death. 

You can contribute more compared to a SEP IRA, avoid the UDFI tax on leveraged real estate, and even borrow up to $50,000 for other needs.

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

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.

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 

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.