You definitly got a deal on that one!
Don't worry about the crankshaft end play believe it or not that is about normal for those things and if everything is still tight (apparently it is) then your compressor may last a long time. Considering how fast it builds pressure I would think that the total time on this outfit must be fairly low and that motor problem may have been due to running in a dirty environment, the clogged air filter would indicate that also but it would seem the pump survived without undue wear. I would suggest changing the oil in the pump again after an hour or so of operation and maybe again in another couple of hours to help remove any stray metal shavings left inside, after that you should be OK.