Our plan is to use my HELOC to fund the down payment, closing costs, minor refurb items, and furnishing the STR. 

There's a roommate currently left that is stealing all the items of the deceased woman that would probably need to be evicted or cash for keys.

One possible arrangement might be for them to serve as the trustee for a land trust with the minor as the beneficiary.Honestly, though, I'd recommend you spend these remaining months getting as well-trained and knowlegeable as possible in your chosen real estate specialty, and then hit the ground running the minute you turn 18 (assuming you don't live in Alabama, Nebraska, or Mississippi)!

Our plan is to use my HELOC to fund the down payment, closing costs, minor refurb items, and furnishing the STR.

The low-hanging fruit is gone, but if you're willing to work hard by getting off the beaten path and overturning a lot of rocks, you can be quite successful.And there are several resources - quite a few folks here on Bigger Pockets and the many specific BP posts and forums from those knowledgeable Investors & Owners, your State Self Storage Association, podcasts, You Tube Videos, and some of us even have written books and/or have meetings and trainings too.In other words, there's quite a bit at your disposal. 

I know of several areas in my markets where something as simple as crossing a street or train track can change values by hundreds of dollars.

Are there some items that have been successful for others1.

(I make about 40k a year and have pretty good credit, and my wife is still building a clientele with personal training and nutrition) I really wanna get like a duplex or quad but starting out I can only seem to find 500k.

Mind any potential code violations, deferred maintenance, and your big ticket capex items(re-paving parking lot, loose handrails, amenity repair, roofing, scope plumbing lines, etc)It’s unclear to me if you’re buying this with your money or other peoples money.

The more you do this, the better you will get at knowing rehab big-ticket items vs cosmetic fixes.Best to you!