A sale, may or may not create taxable income depending on the basis of the property and whether they utilize 1031 exchange to roll proceeds into another property.In general, REITs are stable consistent dividend yielding investment instruments.

One is "I found something new nobody would have seen" and the other is "I want to re-deal this contract every day up to closing" or worse "Me and my agent have no idea there is a 10 foot hole because that's how observant we are".

People are buying them everyday, you just have to make a lot of offers, and be a decent negotiator.

@Joe Villeneuve gives a good basis to start with. 

Imho, you should find an agent that only does investor deals, and you should expect to receive a hand picked list of properties on a regular basis.

There seems to be quite a bit of work to do, but I feel like I can get it done in 3 months if I work on it every day and weekends (which is no problem for me).

Adding even 1 unit is worth multiples of what chasing an extra 0.25% on a refi is worth on a monthly basis.

I eventually transitioned to Airbnb and rent the place out on a nightly basis.

I am there on a weekly basis. 

Also, does cost basis change every year for improvements or added only when the property is sold?