How many spaces can I get?
Coz you got a fever and the only prescription is more breaker spaces!
I have seen so many panels in this forum where someone has a 32-space and it's wedged solid. You cannot have enough panel spaces.
Some panels advertise "20 spaces/40 circuits". That's smoke and mirrors, they are relying on double-stuffing each breaker space. But these days, almost every new or remodeled circuit needs AFCI or GFCI, and those breakers take a full space. Consider only the "spaces" figure.
Now some things particular to homes in rarely-freeze urban California.
- Heating infrastructure is modest, with many homes being ductless and using an Empire wall/floor furnace or electric heat as the only heat. So it's not uncommon to have five 240V breakers (10 spaces) just for heat.
- House values are insane, and many homeowners are in hot pursuit of the best resale value. Which causesa lot of remodeling, and that tends to be deluxe. Wiring demands are in proportion. You can have 4 circuits in a bathroom (floor heat, other fixed loads, 2 receptacle circuits) or 4-5 receptacle circuits in a kitchen.
- High disposable income leads to more gadgets. Atoms are the new bits, Techshop went bankrupt, and that means wood shops with 240V tools, 2 breaker spaces per tool.
- due to conservation, Californians love on-demand water heaters and electric or plug-in hybrid cars. Interest in this at the Federal level has slacked off due to the political redshift, but not in California.
- Conservation also drives a lot of solar, so 2+ more spaces for that.
- Tesla PowerWall. ??? spaces.
Can I get a 100A main in this 200/225A panel?
Any panel remotely big enough will have a 200 or 225A backplane. And most likely a 150-225A breaker. You'll want the big panel and change the main breaker for 100A if that's what your service is.
The big main panel will also greatly simplify any future power service upgrade.
Keep in mind many "service upgrades" amount a new meter only. They know what your service drop size is, and they have the smart meter tell them if your usage actually increases enogh to need a bigger service drop.