Mine-worker is another term for miner, yes. There may be subtler shades of meaning but that's about it.
Mine-captain doesn't seem to be as common as "mine captain", and isn't used in all regional varieties of English. I'm not quite clear exactly what the job is, so it might be the same as is called "foreman" in British mining.
You could probably coin an awful lot of compounds with this sense of "mine", but I couldn't say how many are attested without doing research that you could do yourself just as easily.
As to 4, why does English use words with Germanic roots for some things and French roots for others? Actually, we know why for some of those, but I hope it illustrates the point. For that matter, why do we have the word "window" which does not resemble the word with the same meaning in neighbouring related languages? When terms are coined, there is not always a good reason why someone chose one over another. As a word gradually becomes generally accepted, there my be any reason, or no apparent reason, why one new term gains traction more than another.