@Leo Chun I'd start with a number in mind that you'd like to achieve on a percentage return basis then start analyzing properties in various cities you might want to invest in and see where the numbers roughly pencil out to, then reassess at that point. 

We're a little wary of California's great investment opportunities as the market seems inflated and the percentages seem lower generally but surely there's opportunity.

I like to use actual numbers versus the percentage factors.  

Clairemont is probably also the most central suburb in town as you can access the 5, 52, 805 freeways all very quickly.San Diego has the lowest murder and robbery crime rates of any city in the US over 1,000,000 people in the US:https://en.wikipedia.org/wiki/...It's percentage of people with Bachelor's degrees and higher is extremely high, and SD is very expensive.

Based on what I've read online (see https://www.biggerpockets.com/blog/2016-02-21-tax-implications-house-hacking), I can treat the percentage of the unit that I am living in as my personal residence, and the percentage of the unit I am renting out as the rental portion.

It's flat fee based, not based on percentage.

Is it a percentage of your equities/stocks portfolio, or is it a flat rate of your overall net worth?

Or do you find the person putting down the equity usually wants a larger percentage if it isn't a labour intensive property like a fixer upper or BRRR? 

Hello I want to know if this would be legal, what If I were to find an apartment owner to give me a percentage of my down payment for the bank say 10% and I pay the other 10?

To determine how much money you should save up, I would take a look at the local real estate inventory that you are interested in and save a percentage of that.