Yes, definitely worth paying for a month of AirDNA for that area. Though, keep in mind, things are very much in flux right now, so I don't know that I would trust AirDNA's recent data.
If it's legal in your area (please confirm this before you go any further), you could very easily manage a short term rental on your own without a property manager. You'll just need to develop the systems for dealing with guest communication, cleaning/turnover, repairs/maintenance. All very possible to do with a little work, it's just a little bit of a learning curve.
The medium-term corporate rental market is a little harder to break into, and a property manager who specializes in this might be advantageous. Again, not impossible to do it on your own, just a learning curve and ramp up time.
A larger unit will typically bring in more revenue, depending on the competition in the market. Is it possible to rent the unit as both a split unit and a combined unit? We see that with a lot of savvy operators in seasonal markets. They rent only the larger combines unit during the high season, then split the units up into smaller units during the low season.