1) That would depend on the person doing the learning and the availability of tutorials and/or training for the program. Not everyone gets the hang of it quickly, some take to it like a duck to water.
2) Businesses that manufacture or construct often make use of physical prototypes, both for design analysis and project approval with the client. Some promotional companies make use of models for sales purposes. Some companies make use of printed items as keepsakes, team/employee rewards, or inspiration for upcoming or ongoing projects. Many of these uses have been around for a long time, but have been produced by other techniques.
3) It already is accessible and is occasionally necessary.
4) I have no idea, but I'm guessing it depends on what is being modelled, what the budget is, and what kind of end result is expected.
5) They submit them to companies for printing, or buy a printer of their own. (Much like printing on paper - go to a print shop or buy a printer of your own.) As for which companies - this is one of them.
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