As much as you say “repeat business”, unless you have a track record of a lot of deals, you don’t have the ability to promise this and should treat the first deals as standard sales.

That should put you on the right track.

Someone with a track record in MF? 

I'm tracking mortgage applications as a 1st read.

If you want to focus on the Plumbing business while generating double digit passive returns on your cash, I might even suggest being a Private Lender to a successful Real Estate Professional with a proven track record in the industry!

I wonder what I can use to track the ceiling that is below the roof to catch a leak before it becomes a major issue. 

And track your expenses!

For market prices, 2-4 unit properties are primarily listed on the MLS, so you can search that, or realtors have better comp tracking you can utilize if working with a realtor.As for rents, look around on Zillow, Craigslist, MLS. 

You have found the right place to learn and make some $$$, most important for Private Lending is your track record so be prepared to bring some more cash into your first few deals with you.

Being that mortgage rates tend to track 10 year Treasuries, you should call your banker today to see if it makes sense to lock in a low rate on your primary residence.