I know this is not particularly cost-effective upfront, but hindsight is 20/20.I've heard of the "6 month rule," when it comes to cash-out refinancing. 

I am looking for advice on effective list sourcing and marketing.

You’re effectively paying about 6.5% to borrow.

If so... how does it work, how effective is it, do you have any tips and would you recommend?

It sounds too simple to be effective but a quick "johnson county short term rental" google will get you everything you need.

It is effective on March 4, 2021, and will replace the Homestay regulations. ...General InformationShort Term Rental regulations apply to dwelling units that are used for overnight lodging accommodations that are provided to renters for no longer than 30 days for compensation.

I’m aware now that the ARV is going to be based off my markets cap rate and NOI but since there is no track record of previous income as an 8-plex how would that play an effect on the ARV or acquiring a commercial cash out refinance loan?

Based on the comments, it seems like knowing how to hire right and bring in a strong team is one of the key pieces to getting all the areas you mentioned taken care of effectively.

Have you gotten any feedback/recommendations on good cost-effective amenities for your STRs? 

I don't believe we want to look at a cash out refi as we do not want to increase monthly payments on the home, effectively negating our rental income.