I like to buy in order, RUN BOXES!! Boxes are important to paige's melee because they are affected both by Weapon damage and Spirit power, both of which can be upgraded by the gold pots.
Mid Game
Max out your 2 and your Ult first. Stunning is important because it allows you to still hit players that are conditioned to parry, given you have the timing down
Upgrades
paige doesnt really have a "late game" because her abilities are more affected by general stats rather than tier 3 and 4 items, I just bought whatever seemed good for the match