I can go Home Equity Loan route: HEL would equate to roughly a $600 monthly payment (dependent on rates).

I'm okay with a high interest rate up to 15% because I can still breakeven on the mortgage but not sure how to finance this deal without losing my initial payments

It doesn't help that interest rates are relatively high compared to the last few years and seem to be going up with the new inflation news and such. 

In this case, since they are borrowing their payments, these would get added to the principal balance each month, and interest would be calculated on that.If, for example, the interest rate on the note were 10%, they would implicitly be borrowing their payments at that rate.

Only do that though if you can pay it off or get close to paying it off within a couple of years before the interest rate changes. 

Typically this means they will take longer to close, may not have all the information for the companies they work with, and most hard money brokers get their money by taking an existing product and adding extra points to pay their fee.What is your investor success rate?

Also, can you calculate your cap rate to get an idea of your rate of return. 

Been looking into building out an IDX lead generation website and I stumbled upon software called Mashvisor, it claims to integrate into your IDX website and calculate Cap Rates / Cash Outlay, Etc etc.

There are builders that are offering really low rates.

The benefit of this is that you are not paying Hard Money rates so in long term there is a lot of savings going this route.