Personally If you like your current residence and hope to stay there long term I would forgo major improvements on my primary and use all investment savings to make you more money and cash flow. 

If these houses have stable long-term tenants, I share your concern.

Prepayment penalties- usually 1-5 year terms.

The process is easy:1) You’ll receive a disarmingly simple one-inch-thick three-ring binder containing your plan documents.

The decisions and actions you make today can lead to incredible long-term benefits, so it's great that you're starting now.A good starting point is connecting with a lender that aligns with your goals.

Just in case.Ultimately whatever correlates with your future plans but a solid way to build long term wealth.

The only item I would suggest is double check the payment terms of the your HELOC... in particular, can you pay interest only or are you required to pay a portion of principle each month on the amount utilized.

You lose all of the control and these are long term investments - but in my experience the returns match what I had on the active real estate and I am hiring professionals to manage the assets.  

I’d love to hear more about what you’re targeting in terms of property type and location.

Make a simple spreadsheet or written list with the features of each and see which ones appeal to you most.