don't rely on autotracing.
autotrace could be used on really well delimited colors raster files. but it's not reliable at all on the major part, and will need more tweaking and editing than from scratch tracing.
for vector tracing, try to start with easy characters it's all a mater of positioning the correct "tangent" to the part you want to trace.
the
frostillicus tutorial is one of the best starting point if you want to try.
before going to trace Metal Slug art, that are pretty complex I suggest trying to trace some easiest art, eg the Puckman marquee, Road Runner marquee (this one have some color gradient that will present small difficulties, but the tracing is easy), the SpaceAce marquee, or some individual characters taken from flyers or any other good source.
just try to start with easy parts. few colors, few path and smooth curves. you'll see that vector tracing is not hard, just time consuming.

NB 2 years ago I did not even know what vector art was.