As far as your pet shop urging you to feed live, it might seem that either they make more money selling live rodents than dead ones (which in many cases is true) or they just have that idea stuck in their head, either way they make more money and keep you coming in the store more selling you live mice, so feed it dead its better for the snake because the cell walls are already broken due to freezing, facilitating easier digestion and you can buy more at at time and save gas.
I keep my kings on cypress mulch and only take my very small ones out to feed them in a separate container until they are larger to eat in their cages. My kings love to make holes in the mulch, it looks nice, and its only 2-3$ for a 2 cubic foot bag at the local warehouse hardware store. Its also just as easy to clean as aspen, and its a darker color, which appeals to my eye a lot more. For hid spaces, I use 6" azalea pots that I knock an opening out of, and they seem to feel quite safe and they can easily shed on the clay opening.
I feed my 4' Cali's 2 mice every 2 weeks, now from reading what other people have posted so far on here, I should be shut down for cruelty. However, my snakes are fat, and when I hold them they are solid and I can't feel any bone if I tried. However, when I want to bring them into breeding shape or just after breeding, I feed more often and more mice. I have seen many Corn snakes with fat blobs on them from over feeding, so I watch my snakes carefully. I also feed them retired breeder mice from my local mouse breeder down the street which are usually larger and have a lot to them. My Gray bands however, will only eat one mouse a feeding period, when they have eaten more, they have regurgitated it. So basically I watch my snakes behaviors- and your snake definitely seems like its HUNGRY for more, so feed it. If yours eats 3 mice a feeding great, but just watch its bulk also. The point is, don't just rely on schedules, let the snake tell you by its health and behavior when it wants to be fed.
Hope this helps, and enjoy your Cali, you got a great snake to start off with!
I attached a pic of one of my Cal Kingsnake 20gal long habitats with cypress mulch, though I realize now it looks kinda messy but the female Coastal Cal that lives in it, is very fat, healthy and seems to have a low stress level due to her calm movements.

-----
1.1 Newton County, IN Bulls
1.0 Texas Red Bull
0.1 Kansas Yellow Bull
2.1 Red X Yellow Bulls
1.0 Medicine Hat, Alberta, Canada Bull
1.1 Carolina Northern Pines (M from NC, F from SC)
1.2 Henderson County, NC Black Rats
1.1 Gray Banded 'Blair's' Kings
2.2 Coastal Cal Kings
1.1 Speckled Kings, Harris County, TX
1.1 Eastern Chain Kings (M from GA & F from NC)
1.0 Hogg Island Boa
1.2 Ball Pythons