Each story arc is pretty self-contained. It's not like other long-running shonen manga where you have to read 400 chapters to know what's happening.
For example, in the third story arc Stardust Crusaders , the protagonist of the second arc is a supporting character and the villain of the first arc is the primary antagonist, but you aren't missing anything if you haven't read the first 2 arcs.
It will probably cost a lot if you buy all of them, but you have the freedom to jump around.