We bought it with a HELOC on my mom's primary residence for the first $40k, then hired a contractor for demolition and major renovations, did cosmetics ourselves and used more heloc money totaling $60,000. 1 year later we listed it on VRBO and AIRBNB and refinanced the $100000 into a fixed rate mortgage.

Otherwise, HELOC is a great resource.

A Heloc on my primary residence was where I started, and I was able to use all my own money. 

We do them, but they aren't cheap and your LTV will be lower that a HELOC on a primary residence.

No, I put 65,000 but its probably worth 140,000 I'm trying to get a HELOC to do some renovations, then rent it out in April.

I do have a HELOC for a worst case scenario--maybe this is also naive. 

A lot of the time, the HML 2nd secured by the high equity primary residence would end up getting paid off in short order with via a HELOC, so there'd have to be points in it upfront for the HML for it to make sense.

You're already at 90% LTV so a HELOC will likely not be viable.

If my primary residence has $500k HELOC, could I use it to purchase a 2nd primary residence and rent out the first one?

I also can go higher prices by tapping into a heloc for part of downpayment.