Just keep in mind that this is what I would do in your shoes and not necessarily the one, true, and right solution.

You will need to have a great marketing plan and stay with it for a few months before you find a real deal.I come across so many wholesalers who start out thinking that it's an easy way to make some quick money, but that's far from truth.If I were in your shoes and my goal was to make $5,000/month in passive income, I would work my way back.

For $5K you can take over the $15K contract, stepping into my shoes as the buyer.  

If it was myself in your shoes I would really study the market there ...ask around, Internet search, talk to property managers etc. to find the best neighborhoods for both appreciation & cash flow.

What would you do if you were in my shoes?

Anyone that needs three can live in four and have an office, storage, exercise room, etc. 

One unit is being used as storage unrented, and needs completely redone.

how did others in my shoes start out?

I would follow the suit with the rest of the neighborhood... maybe that area doesn't care for outdoor storage space.

Once your ready to put your investor running shoes on, you might want to check out the local real estate club.