Mything the legs wasn't worth it currently imo. If you really wanted to myth something, it should have been the nightmare or frantic/nightfall. It is advised to myth the legs after done mything the more important stuff (torso, weapons, modules), as the legs just give a 'small' amount of extra hp + dmg.
Anyways, you already did it, so that's that. (I myself on my account did not myth anything for a few months after start. First i got everything to level 40, then grinded a ton of level 20 power kits and when finally decided, i did it smartly.)
GoldenTX already wrote nice advices, but i'll say that when upgrading modules be sure to prioritise things like the heat engines and the energy regen ones. They are your best mods currently.