They have a handy feature where you can manage multiple accounts for each of your properties but only need to remember one login.

I plan on hiring a general contractor ( like many do) and then hiring my property manager to manage him. 

It seems to be a very tightly managed building, which is typical for Ocean City, Maryland from what I have heard from my real estate agent and lender.

Since I will be leaving my corporate job and effectively self-employed as I manage most of my MF portfolio, can I roll my retirement savings into a Solo 401k and invest in RE with the money?

My PM company does manage some there though.  

It's saturated now and management fees are high for STR, up to 25 percent.

Could you self manage?

If you consider out-of-state investing, I recommend reading “Long-Distance Real Estate Investing: How to Buy, Rehab, and Manage Out-of-State Rental Properties” - I found it to be very helpful when I got started investing 2.5 years ago.

I manage & do all of the setups because I'm local. 

In my market, buyers are looking for about 12% or more in gross rental income relative to purchase price, so if you have a $500K property that's only doing $40K/yr under the current management, don't post rental history (though most buyers will ask for it, so be prepared to explain why it's performing the way it is).Also, network with agents who specialize in STRs.