I'd be curious if your rental income from your other properties was considered to supplement your net-income from your self-employed jobs when the other lenders tried pre-qualifying you for a conventional mortgage. 

It's not a huge cashflow difference and since we don't touch the income it builds up a reserve to cover unit turnover etc but if you plan to use that income to supplement your income then I would do 30-year to create a faster reserve before you draw against the income.

Without knowing your job situation, retirement planning, etc. there are a lot of different variables at play here. 1) Renting the property would theoretically generate cash flow that would supplement your monthly retirement income.

Solar supplementation is expensive and takes years to pay back  

That is some nice supplemental income when you are retiring, but it all depends on your personal situation and what works best for you. 

I'm not 100% sure what viewpoint you're coming from with the question but here are a few possible scenarios you may be considering...1.) you're inexperienced as a party to a real estate transaction, and you want to gain knowledge while also setting yourself up to earn income and save commissions.2.) you're an experienced investor and have been a party to several deals, and you just want to save commissions, get easy access to properties, all while helping the occasional friend/fellow investor as supplemental income.I'm guessing you're closer to #1, and your intentions must be abundantly clear... do you just want to avoid commissions, or are you in it to learn and grow in the business? 

You also should have loss of rent coverage with your insurance that can supplement your loss of income during the cleanup and fix up. 

Mobile seems perfect for the small stuff, for bedroom, bath, kitchen, dining where you  can install  appliances, hvac, electrical, and plumbing in the factory - supplemented with  a kit based barn style garage and storage with large open plan living room above.   

In my mind, I need to supplement my income or find a higher paying job. 

Having the HELOC would be a supplement to these reserves, but I would avoid using it as the source of a down-payment as the interest is variable and often much higher.