Whenever I am having an issue with financing, I normally reach out to local institutions.

But since you will be able to finance with LTVs, potentially higher leverage may be used and can scale the portfolio faster with the right strategy. 

I can run some numbers and share some options on the financing side if you like.

Simple answer - yes you can alter your funding source after putting it under agreement if you chose to use a hard money lender instead - i would just communicate with seller that hey I was going to use cash (assuming you have it from your heloc) and instead will finance some of it but let them know its not contingent on financing.

Which BTW most of our closings are subject-to the existing financing, so we have little cash into the deal, just the arears and the closing costs.You find NOD and pre-notice via;   realtytrac.com / equitydepot.net (if they cover your area). 

You must have your personal finances in order before you invest.

I'd need to finance with hard money.

You can theoretically have a higher rate from one lender with lower origination fees and total finance charges may come in lower.  

The financing and management of each are very different.

This is less risky and can earn you money quicker to use to buy investment properties.Also ask burnt out landlords if they would sell with owner financing.