new here, and thanks for all the info

I've learned so much for the past 2 months just looking around, researching, and finding everything I could with solar. I wanted to go the route of DIY so badly but CA makes it so hard with all the permitting process. On top of that my roof is basically 30 years old and my main service panel supports only 100amps. I think I am going to cross off the DIY and just go with the pros so they can do all three at the same time. I've been doing some price calculations and rebates and it's a difference of $3-8K if I was to do it my self minus the headache.

Now, if I go with the pros and they install a system and get it connected, how will the city/pge know if I added some panels and batteries to my system at a later time?

Some of your components will determine if you can later add the battery bank and more panels. For a grid tie, you may only need an inverter that feeds directly back in to the poco lines. For using the solar power yourself, will need charge controller, storage and and inverter.

If you can get an all-in-one box that is CA compliant, then might be able to add on later without much trouble.

You might also consider installing a modest soar array at first. But keep in mind the charge controller and inverter or an all-in-one will need to be large enough for more power when you add to it.