I am having a hard time for finding insurance for an 11 unit  apartment building in California.

With that said, if you are talking about a standard "value-add" people have been pitching the last 5 years (put a lipstick on the pig, renovate each unit, minor amenity upgrade, and pencil in rent growth), 100% return in 5 years would be challenging given the current interest rate environment and that the rent growth rates have come back to reality. 

What tools are popular go to's for comparing US Real Estate Markets in the interest of choosing multi-unit long-term holds towards building a Real-Estate Portfolio? 

Where it does calculate out to an ROI is in other states where you can buy a 2-4 unit and the other doors allow the cash flow.

My most expensive unit was 300k and it generates 70-80k.

Their lease will be ending in 8 month from now.I’m not sure how many units there are total.

I have learned by buying many HVAC units and replacing multiple roofs :)Call a few HVAC contractors and ask - they will be reluctant to give an estimate without seeing the property, try explaining that you are an investor and are simply trying to model some deals.

Right now, I'm house hacking - owning a three-family house in NYC and renting out the other two units.

We require guests to load and run the dishwasher, remove all food and trash from the unit, and have guests text when they depart.  

It might also be possible that while you are living there you can upgrade your unit some to where it could generate a higher rent when you move out.