It can be easy or tough. It depends on how rusted it is and how much patience you have. Start off by wire brushing then sanding the entire length of the axle. Especially near bearings, sprockets brake disc and wheels. The start soaking the axle down and bolts with a high quality penetrating oil. Every day a couple times a day give things a couple of taps with a hammer and more penetrating oil. Things should start to move in a couple of days.
It would be easier if you kept this in your build thread. Good luck!