I am not sure what type of real estate investing you're considering, but it sounds like, with your family and busy job, you won't have a lot of time to be hands-on or personally involved. 

A real estate business can also potentially generate a SOLO IRA or something like that. 

Most of the time a newer or unsuccessful agents will host open houses as they build their book of business.

Due to the nature of the shorter lease terms, I am spending an excessive amount of time updating my Excel spreadsheet, MLS, business website, Airbnb, VRBO, and other platforms.

Don't apologize, don't explain how the 'chosen' tenant was more qualified than they were, wish them well in their search.You're running a business and you've made a business decision. 

They were selling on pro forma, but the market and the debt market have shifted, and it's aa lot harder to achieve higher pricing with lower rents.We've purchased over 2,000 units, and the simple answer to the question is that they are either mom and pops and run their businesses with ZERO KPIs, they do not want to risk losing tenants if they raise rents, and they don't treat their asset as a business.When you take over, it can be difficult to get rents to market if they are very suppressed.

I'm the sole manager of the business and the properties.

If the proforma has the rent roll at $1400 a month, there is a discrepancy that could lead you into a bad assumption on your business plan.Also one caveat, be aware of physical delineations around the area like bridges or railroad tracks or a canal. 

All too typical park owner who took all the profit out of the park without reinvesting in the business then wants to sell you the potential he was too cheap to invest in. 

Having the seller carry a second is not a problem for the first, as long as their business with you is finished and the loan has closed.