well I'd define small as anywhere from 1-6. legal for most patients in Cal averages 6 plants per patient so maybe start with 6 or 12 depending on how many recommendations you grow with. I know of a hill side out my way that has 500+ all in rows but who knows who those guys know in with the local smokies and who's getting paid off it. I'd say just start small and work your way up. cal's definitely the place though if you want to do it with the law somewhat on your side. but just like it is in most places, don't step on any toes
Many of the big, somewhat visible grows in Humboldt, Mendocino and Trinity are pooled MM licenses from all over the state with landowners and growers (sharecroppers) acting as caregivers and taking their cuts at harvest time. That's why CA dispensaries want MM patient caregiver status from their weed customers.
Stepping on toes anywhere weed is grown can be very dangerous. Most guerrilla growers in my part of Oregon live with their crops several weeks before harvest, are heavily armed and not happy with hikers and such wandering in their remote forests. The common tactic is taking driver licenses at gunpoint with the threat of if busted they have an address for future reference. $100-200k grows are not to be trifled with.
Most of those growers were born and raised in those areas, know every square foot of territory, every game trail and intersect intruders long before they ever reach growing areas. It could easily be compared to the old moonshiners and It's not a vocation recommended for noobs.