I have a potential tenant who is requesting to pay rent by money order rather than through the RentRedi platform. 

Rock solid rental while the money is in the stocks doing double duty as the principle investment as well as your down payment equivalent.

Absolutely not.According to Heather and Brandon Turner's book, the fact that they want to put so much money up front means they are trying to distract you from something else they don't want you to see, and hope that offering you enough money will accomplish that.

How tight is your money game?

Only problem is, I’d like to get as much of my money out of it as possible.

With baseball, you start making money once you reach the big leagues, in the minor leagues, every player's salary ranges from 34k to 39k.

but that money is tied up.higher risk: borrowed money. 

Booking.com is even more expensive than VRBO/ABNB, so you will likely be costing yourself money for every Booking.com reservation.

If your debt is student loans at 6-8% interest your best bet is to pay them down/off as fast as possible as most investments will achieve a similar result but that is gross (before taxes) not net.  

Especially in a big money/high demand area like you're in.