a fuel processor is going to change your fuel air mixture from the factory setting to some other setting. overriding the factor computer adjustments.
this generally has the effect of making your bike run better. assuming you set it correctly.
my thoughts on them for cruisers are get one of the autotuning versions. a couple hundred extra 1 time fee. saves ya ever having to get someone to tune it for you. and adjusts when you go from sea level to 5000 feet ( like climbing I-5 out of L.A.)
otherwise there are prebuilt maps for various intake/exhaust combinations per bike that you'd download and copy to them via your computer. and some simply have adjustment dials or buttons to select preloaded maps.
the general consensus is it is not required ( but still helps) when only swapping pipes. but if you dink with your intake ( k&n filter, hypercharger, tornado....) you need one.
they'll run anywhere from $100 to $600 depending on what you choose.
powercommander 3/5 , cobra fi2000, bully fp, fuelpak you'll see all of these referred to in various mod lists.
they're fairly easy to install and a pretty common mod once ya get past things like seats and grips.
as for pipes. my suggestion is spend some time on youtube looking at vids. they'll give you a general idea of sound.
alot of aftermarket pipes have removable and repackable baffles to change the volume but it will change the sound too.
cobra, vance and hines, hard krome, cant really go wrong with any of them, but there are plenty of other good manufacturers out there.
