Then divert the income from the rentals to pay down the HELOC, and then focus on paying down the principal on the various investment properties’ debts, ideally creating a snowballing effect where multiple properties help pay each other off.Do people just “bite the bullet” and accept slower business timelines when they only have enough capital to purchase a single property at a time?

Also, many utility companies have services like energy audits (free) where they come and evaluate the unit and let you know where energy and heat loss is happening.

Even if nothing comes of it, it's a little energy boost, and hopefully by sharing, I can offer some encouragement to anyone who might need it.

My two cents, and more importantly to save you time, energy, and capital; I would potentially consider looking into other side hustles to gain additional income.

Recently had an "all cash" applicant not disclose a divorce, foreclosure and subsequent bankruptcy although thanks to knowing the process was able to get the picture and dodge the bullet. 

So biting the bullet and purchasing two for your 1031 might make sense if you anticipate that.

I like that energy. 

Smart thermostat or programmable is always a good idea for energy savings (more important if you are including utilities).

We dodged a bullet.  

I recently heard about the energy rebates from state of New Jersey for new construction like $2000/Unit.