According to the US census data Los Angeles, CA county population declined 3.5% in the last few years as you can see here:(Data from April 2020 - July 2023).But Real Estate prices went up in that period 25% according to Zillow (From $665,868 to $834,772).Rents went up 18% (From $2,380 to $2,827).How that can be?

Period.5.

. - A $300k HELOC on the second home, at prime + 3% with a 20 year draw period.  

Sometimes they include annual increases and sometimes they are flat for extended periods of time so it is very important to understand how the base rent is structured prior to buying a deal.4.

The 3xs monthly rent rule is an outdated calculation from a time period where income to living expenses evened out.

2nd questions; I Just got pre approved for a non QM product: 20% down, 8.25% interest rate, 12 month pre payment penalty period, 2 points, and Conforming Conventional product: 25% down payment, 8% interest rate, no pre payment penalty, 1 point fee. 2-4 unit in Ohio.

Does this affect their ability to live in the house or use a part of the house for an extended period of time? 

Having a private party as the lender also offers more negotiability, I've found many private parties willing to extend terms with either bulk installment payments or a higher rate of return.

As a follow up, is 12 months the minimum owner-occupancy period prior to a refi and change of primary residence?

Is the holding period calculated from the purchase date to the sale date?