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

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

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.

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 

Diversification into multifamily also lowers risk compared to a single rental, as vacancies won’t affect your income as drastically.3.

Take a look at the pictures, is it higher, lower, middle quality compared to yours.

Appreciation = Specilation/Gambling.We have little control over the factors that affect it, albeit for making improvements that will force it to compare with other likenpropetoes that are in a higher bracket.

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.

There are plenty of deals in Philly on and off-market from wholesalers, who are pretty decent in Philly compared to other places.You will need to get your GC license here and learn the permitting process and necessity here as well.