I am new to the real estate investing field and am seeking advise between choosing a HELOC/Cash Out refinance loan for funding.My primary home is paid off and valued at approximately 600k.

Indeed, you would have a higher interest rate for this commercial loan.

I used a conventional loan with down payment assistance because the appraisal process is less strict than FHA or USDA and the bathrooms were barely functioning.

For investment properties, you can get a private money DSCR loan or hard money loans that are asset-based. 

90% of my clients are using the 10% down second home occupancy loan to buy in the STR asset class in all 50 states.  

When using and FHA loan, if there is a non-occupant co-borrower that is a family member, on a 2-4 unit the max.

These types of loans consider the anticipated value of the home after improvements or renovations are completed, which can be particularly appealing for homeowners planning significant upgrades.

I'm a Mortgage Loan Originator and my company has some great investor products.

Yes, a DSCR loan would only require minimal documentation from you.

We did purchase the duplex with the new conventional Fannie Mae 5% loan and it came with PMI of $71/month.