We blast 500 - 5,000 messages a day from one number in multiple markets, and we never had an issue.

(assuming market does not crash etc).

From what I've seen in this area right now, it seems like you'd have a hard time paying market LTR rents and making a good spread. 

I use Facebook marketplace as my way of marketing my rentals.

Market Conditions Aren’t Always in Your FavorHouse hackers often assume their property will appreciate and rents will rise, but that’s not always guaranteed.

There's no real hard and fast way or only 1 way or doing your first 2 points. your subject line suggests you're not looking to go to a large shop like a JLL or a CBRE which honestly I don't blame you those offices are usually pretty bloated.As far as monthly costs, if you are going to individually get a costar or other such license you are probably looking at $500-$1000 a month pretty easy in overhead once you have office dues, mls dues, marketing, etc. 

Also, if you're having trouble finding inventory in your market, look for single family homes with accessory units or even mother daughter setups.

What is the average spread in the market(s) you are in for flips?

I would recommend you focus on a couple neighborhoods that you would like to live in; and familiarize yourself with that market.  

Is this similar in your market?