If you grow up around it you don't even think twice. But to come in new it can be overwhelming. But fortunately, the answers are pretty easy.
1) Most Chinook return to spawn on a 4 or 5 cycle. Jacks are young males that have returned early, usually after only 2 years. They are smaller, and tend to be more aggessive.
Springs/Kings are a slang term for Chinook. Springs because they begin to return in the Spring, and Kings (and American term) because they are the largest of the salmon. Most species have a slang term. Coho are also called Silvers. Sockeye are called Reds. Pinks are called Humpies, and Chum are called dogs.
2) Most fisherman keep a female expressly for the eggs. They are one of the best baits for salmon, as well as a large number of other species. That being said, with each female carrying between 1500 to 3000 eggs, I find this enough for one season and will switch to keeping males. I find they taster better. Others who fish more often may need more.
3) The number of marked fish varies by system. In a system like the Vedder, which is managed as a catch and keep fishery a majority of the fish will be from the hatchery. But I personally don't think there are too many systems that don't have some marked fish in them. Salmon explore. I have known several fisherman that have caught clipped coho in smaller systems that have never had a hatchery on them, and are not easily accessible except by boat.
4) There are numerous volunteer options available in the LML. South of the Fraser there is the Semiahoo Hatchery near White Rock, the Tynehead Hatchery in North Surrey, and the Nicomekl Enhancement Society in Langley. Those are the ones I am most familiar with because I live in the area. But I am sure others on here can direct you to something closer to home if those are too far.