The complex consists of 4 buildings with 2 units each, current rent is $650/unit for a total of $5200 in rents.

The platform I invest (gamble?)

You should utilize resources like BiggerPockets, build a team, and use online platforms to find potential properties.

I have a "friend" that has an apartment unit that consistently has bad tenants.

Stay consistent, stay humble, and don’t be afraid to make mistakes—that’s where the growth happens!

If there are any platforms offering more attractive terms on the HEA than the HELOC it could be an option. 

Denying Based on Court RecordsYes, you can generally deny an applicant based on publicly available court records, such as evictions, judgments, or warrants in debt, as long as the information is accurate and you apply this standard consistently to all applicants.

I am in the process of buying a small MHP consisting of nine lots with eight of those lots having trailers on them that will be purchased with the park.

We are now offering a limited service option where you would own the Airbnb listing, we would have to own the other platforms we list on listings, however.

If so I'd recommend looking at RentRedi, it's free for pro members and it has a free prescreening application, and also does credit and background checks through the platform that the applicants pay for.