For your seller its an effective sales price of ask - 2% using your assumed $500,000 thats $490,000, a real good offer depending on your market.  

It sounds like a single family house where you will be living in the house(personal use).Therefore, you may not be getting the tax benefits you think you are.Consult an accountant.I am not sure why your sister would agree to this as well, she is losing $170,000 in this transaction and she faces the possibility of you increasing her rent.You also have to charge market rent or close to market rent or it is all deemed personal use.

I’m active in the market and happy to share insights on neighborhoods, financing options, or connect you with resources.

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. 

In the future I would like to run Facebook and instagram ads in a market that guest from.

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

If you get greedy and put #3 in front of #1 or #2 you can get burned like any other market. 

I sold all my SFR rentals in that markets as collecting rent and keeping houses in good shape was just too tough.. ( thats jackson proper)  as I said madison and Ridgeland will be fine..

There is around 500k equity in the property. 150k-200k would get the property fully rented at top dollar with desirable tenants. 100k would get it to where I can rent all the units back out at fair reasonable market rents.

I look every day for off market houses to flip.