I have a seller who has agreed to sell property at a discount, however he has to turn self in to authorities because of domestic violence, I believe with in 20days to do so.

I have had a lot of success with single income families and single moms making a living slightly below the median household income.

I don't think that you use an LLC unless you are building a business to attract investors and that is a more complicated structure with more costs involved and I think you only do that when you have a lot of success under your belt and know how to deploy hundreds of thousands of dollars to millions of dollars with outside investors' money. 

I read some good success stories and decided to create my profile and introduce myself. 

That's all assuming you can get a successful judgement against him.Honestly if he's a creep and not communicating, that may work in your favor. 

I was thinking that they get paid the most when there is turnover, so has anyone been successful in crafting an agreement that rewards for:Tenant longevityShort vacancyKeeping repair costs down (I do want to address issues though)Dunno...

I was successful reducing the tax by a couple thousand dollars on one property a few years ago doing it DIY, but my comps for another were bad and got nothing.https://www.state.nj.us/treasury/taxation/pdf/lpt/ptappeal.pdf

I am also a licensed real estate broker with Nottingham Realty Group and I have had a lot of success helping investors (both local and out-of-state) buy investment properties, repair them, and either lease them to quality tenants (BRRRR) or sell them as a flip (BRSR).

If you don't know what a unit will rent for, you have no idea what you can pay for it and cash flow.I'll leave it at that, but stay focused, be willing to spend some time and be patient, and you should be able to have success here. 

I have had limited success with rent-based Incentives - like 1/2 off first month of rent when you sign the 12 month lease.