Yes, moving your brake pads down 4mm is the only hurdle to clear. Obviously you'll need new tires, which I assume is why you're doing the switch.
As for the rear spacing, I assume it's spaced at 120mm with a 5 speed rear. But measure it to be sure:
http://www.sheldonbrown.com/gloss_sp-ss.html#spacing If you don't want to bend the frame you'll need a new wheel with the same spacing. Fortunately, on most wheels with thread on freewheels you can easily space the hub out to whatever you want. If it's quick release, you might have to cut the axle short if you're spacing it down from 126mm or 130mm.
Originally Posted by
flayz
on a side note, i work at a bike shop so i can perform anything by myself
Er... I hope you're new there. Much to learn, you have.