From BP podcasts, I've heard David recommend HELOCs mainly for shorter term ventures (such as flips) due to the high interest rates (which can be variable) because you can pay back the HELOC relatively quickly. 

The other variable too is the uncertainty in the stock market and general instability in other asset classes along with raging inflation.

It is a multi-variable equation.

If so, any insight you have on how a 2-story unit may / may not impact vacancy and turnover due to variables such as: Complaints from downstairs tenants related to upstairs noise Lack of a garage Walking stairs Living in an ADA unit, if not needed (1-unit has to be ADA per the county) Other?

I have looked into helocs but am concerned about variable interest rate associated with them.

I recommend you do this each year to adjust for utility increases and other variables.

I know there is a ton of variables, but people who build apartments from the ground up, what is your desired return on a new build apartment complex?

I recommend you do this each year to adjust for utility increases and other variables.

In Canada, we take 25- or 30-year loans but then the interest rate is set for shorter periods, typically 3 or 5 years at a time and is fixed or variable.

Typically, HELOCs are variable rates so given the current rise in rates make sure to compare the interest rates you currently have to the HELOC rates ( I would guess they are lower than the CC rates but don't know your personal rates.)