My $0.02 worth answers...
Re: >> How big is Key West? It sounds like its easily tourable by bike?? Or car? <<
Approximately four miles long by less than two miles wide.
Navigable by bicycle, but riding at night can be a bit sketchy, even though rental bikes come equipped with tiny flashing LED lights, front and rear.
Driving and/or parking a car can be challenging around "downtown", not to mention not being able to truly experience the "atmosphere" or the people from inside an automobile. Keep in mind that many (non-timeshare) lodging facilities do not have off-street parking! Additionally, on side streets marked as "residential", you cannot park at all (for locals only) and the ticketing is very energetic, both day and night.
Re: >> Do you know what the distance is from Key Largo to the tip in either miles or hours? <<
Exactly 105 miles from one particular resort I know in Key Largo to the southernmost point "land-buoy" in Key West. Driving time is much less predictable, however, since any wreck on U.S. Route 1 along the way brings things to a temporary standstill in very short order.