cali is cool but south california mostly sucks (i.e. los angeles). but as mentioned, the I-5 is boring and sucks for rides, i've done it several times. the way to go is the 101 down the coast, you can start from upper oregon and hitch your way down and it's amazing pretty much all the way to san franscisco. beaches, cliffs, woods to camp in, easy hitchhiking, etc.
klamath falls is a crew change hub, but it's the only spot (that im aware of) that has a mandatory 2 week jail sentence if you get caught on a train there. it's in the city laws or something like that. so you either need to be super ninja and know what you're doing or pass it up for an easier yard somewhere else.
based on the route you're taking, you're going to either hitch or hop, not both. id do the hitching down the coast first, then come back and do the trains someday when you've got a little more experience under your belt.
it is true there is/was a city bus from sacramento to roseville (and an amtrak for like 10-15 bucks), but keep in mind roseville is one of the biggest yards in the country, probably not the best place to start out your first time riding trains.