Nothing you said is wrong, but organizing among these classes comes with certain inherent dangers which need to be recognized.

1. Students tend to come from a privileged strata relative to the majority of the population, and I say this as someone with a graduate degree. My parents were never wealthy, and I got into college on scholarships; still, they owned their own house, they had some land, and my mother was able to stay home and not work. Money was sometimes a little tight, but we never really felt much of a crunch. This is a basically middle-class lifestyle that a whole lot of people in the US don’t have. A lot of college students, being from the middle class, do have a fear of being absorbed into the proletariat; they may resent the ruling class for squeezing them, but they don’t themselves have much natural solidarity with working-class people. They in fact often see the ruling class and the working class as two millstones grinding the innocent middle class; thus, they are easily led toward fascism.

2. One has to distinguish between types of service workers here. In deindustrialized countries like the US, there is a strata among service workers which can be described as “workers becoming lumpen;” they have the values and general class tendencies of the the industrial proletariat, but from economic necessity are stuck working at Kmart or McDonalds or the like. It is a precarious position that cannot be maintained for very long, but one can often reach these people with the promise of real jobs: “wouldn’t you rather be building a hydroelectric plant on the Mississippi River than flipping burgers?” On the other hand, there are certain service jobs which seem to recruit largely from students, or parts of the middle class who have sunk economically. Luxury boutiques and high-end stores are an example of this. Their employees are not paid well, but I have found that (rather paradoxically), they tend to identify more with their employers than with working class people; probably because they make their money (and at times have a certain status within the service industry) in an artificial market propped up entirely by wealthy people’s spending.

3. The great danger of organizing among the lumpen is getting drawn into the criminal element which tends to exist wherever you have desperately poor people. This happened to the KPD during the 1920s. Very often, party efficiency degrades as a result. Moreover (as Marx points out) the lumpen are easily bought off, since they have literally nothing. Often they are served better by working with sectors of the working class who have a vested interest in never siding with capital; thus one can create extra-governmental structures, and eventually an entire society, which enables people to escape lumpen status.

4. The same things said about students can generally be said about artists, though (as you said) they are certainly important for reaching the masses.