intelligence levels you faster not luck
luck only effects critical recharge rate, maybe effects container loot aswell
trashcan carla will be wandering around drumlin dinner, look for her around there, she also turns up at bunker hill like all the other wandering traders when its her turn
once you own sanctuary carlas circuit is drumlin dinner to sanctuary and back round etc (aswell as her obligatory bunker hill day)
im not 100% sure but i think you need settlers at sanctuary before carla will turn up there?
companions really offer nothing in help gameplay wise other than extra carry, i have been using piper since i got her on very hard/survival with nothing more than her original leather coat (no weave) and default 10mm and im having no problems
in fact not having companions and taking lone wanderer not only makes up for most of the extra carry weight (piper can only carry 165lbs) but by doing more and taking less damage you will be much more powerful than traveling with a companion
really due to their unbelievably annoying AI (getting in your way constantly etc etc) and poor combat skills (constantly shooting walls sigh), you really should have an easier time without them especially with lone wanderer.