I would do some online research into Realtors in your area to see if you can make a connection.As @Michael Dumler pointed out, wholesalers are going to be a more reliable source for consistent off-market properties with margin.

Examples could include but are not limited to installing new/ improving driveways, clearing overgrown trails/ build sites, demolishing abandoned buildings, property cleanup, extending or having utilities pre-approved, etc.

If I am self managing my portfolio, what do I need to check/confirm, and what easily available tools are at my disposal (online, other) to help me do this? 

Listing sites like Airbnb and Furnished Finder, and B2B relationships for referrals, insurance, and corporate bookings.

This site will be for 3 properties to begin with.

Demoed the house, will be building a new house on site.

You can also check their reviews online at Google, Facebook, or Yelp.

Any recommendations of online companies with these services?

Wondering if someone can point me to a reliable resource because the hours of research i've done online did not give me any clear, obvious examples of how to do this correctly.I owned my first primary residence for some years.

I put supplies on the job site.