I save 3% when I list my properties myself but this is my primary.

Keep your w2, save save save, and buy something every year or two or three.

You'll learn quickly, save yourself money and be the most motivated to get the right medium-term rental tenants and the keep it occupied.

So today, I decided to create a rental property calculator from scratch in google sheet or to be sincere, I'm yet to save all up for the PRO member fee.

My projected ROI is 4.5%... so do I purchase it, or wait and save up that money for a bigger down payment on a multi-family property?

Be sure that the plumbing and electrical are all good before replacing walls or ceilings or you could have serious trouble and expenses down the line.Regarding finances: I have used QuickBooks Desktop version (saves a lot of money but does not get the constant updates) for five years.

Save that cash flow up for your next down payment.  

If the funds are in HELOC, a retirement account of some sort, run a similar analysis. 

Hosts that want to make a decent profit get a little skin in the game, and if that means paying a bit for real data so they aren't coming back on this forum in a year asking how to save their STR, then that is what it takes.

Building these relationships will save you time, money and headaches down the road.