As you suggest lowering down payment to buy more properties is one way, although the downside is greater risk in event of down cycle and more time to manage required.  

The lower unit is a basement/guest suite.

A HELOC offers flexibility and lower interest rates, which can be ideal if you’re looking for short-term financing with lower payments during construction.

I have lowered the price significantly this year. 

More equity means lower downpayment.  

However, I made the decision when interest rate was lower and there was support for an appreciating real estate market.

Planned energy-efficient HVAC installations will replace outdated ceramic heaters, reducing tenant utility costs, lowering insurance premiums, and qualifying for utility reimbursement programs—a win-win for tenants and investors alike.Inflation HedgeReal estate is historically a strong hedge against inflation.

Are there any lenders who are lower than this, I've been brokering myself.

Question: Should I collateralize the loan (if using private or hard money), or rely on roll-over loans (to maximize the lower points and 3-4% rate)?

Servicing costs are fixed, rates get higher lower the loan amount gets.