It can be done but you need to pay close attention to current home and new home.

My concern is the investment in Detroit would need to create high paying jobs in the city and those earners to live in the city for change to come at a granular level and be sustained.

I only recommend using a HELOC for scenarios where you'd be able to pay it back within a year.Alternatively, you can just buy another investment property with lower down payment, which is a better interest rate than anything you'll get on a 2nd lien HELOC/HELOAN. 

Another thought - When purchasing HVACs, roofs, tree removal, siding, etc. you can very easily pay "retail" (just look for the biggest ad campaigns online) or you can save 30-50% by being your own GC and finding or going to the crews directly.

So it would not make much sense to put only 15% down if you have to pay an additional 4.125% in points to make it happen.

I agree with @Jaron Walling, you have an opportunity to sell and harvest a profit and avoid paying tax on that profit because it was your primary residence.

I specifically need really user friendly accounting features (including ability to sync with quickbooks and print checks directly from the site/software), customizable online application, and online rent-pay as an option (hopefully with free or very cheap ACH). 

You agree to pay an additional $200.00 lease violation fee each time we determine, at our sole discretion, that smoking has occurred in your rental unit, due as Additional Rent.

Nobody pays me to stay home and meet the cable guy or the appliance technician.

Insurance would cover it, I would pay the deductible, and no assets would be lost.If you are in an area like San Diego where people are more likely to sue, a judge is more likely to find you guilty, and the payout is expected to be higher, you may consider an umbrella insurance policy.