I can’t answer that question exactly from personal experience but I assume since you currently have a furnace that you have a forced air system. Why not just change the furnace to a heat pump? It’s literally perfect for your climate and would provide both heat and cool using electricity and your existing duct work. Additionally, you won’t have to put indoor head units in all the rooms.
Most people prefer forced air systems over mini splits and they go the opposite way that you’re proposing.
In your climate (I was raised in Monterey so I’m familiar with it) you really don’t need a gas system like you have and a heat pump would work great. In colder climates gas is a much more efficient heat than electricity.
I do have experience with gas water heaters vs electric and maybe you could draw some conclusions from that. My house was all electric. I recently installed propane and switched the water heater. I was spending about 40-50 a month on the electric. With on demand propane I’m spending about $5 a month.