In vitro information helps, but there are a few things to consider which affect the results in an actual human, such as the half life
of the drug, its distribution in tissues and fluids, reactions in the body, etc. One great thing about it is it's bactericidal, which is a great advantage.
3) As above, I wouldn't try anything else quite yet. For one thing, sparfloxacin is a similar type of antibiotic (fluoroquinolone) to moxifloxacin, and is actually quite potent as well.