I've played YoshQ a lot, I've MM'd him a few times and played him in friendlies trying to learn this match-up.
Luigi is not someone you can fight face to face so easily, he has the fastest moveset in the game, yeah faster than MK's overall. He can beat us int a boxing match up close so space to keep him out of range. Ftilt, this move is very key in this MU, because of his shield push Filt will push him too fair away, even if he power shields it all he can do is get one jab off before he slides too far for a follow up.
His nair is really dumb, last MM I had with Yosh, I tried to fair nair when he respawned, he DI'd up and hit me with the sweetspot and killed me. Fortunately aura does out range it. Shield grabbing is very good in this match-up but you must do it at key moment's if Luigi does it while rising you can't shield grab him, if he saves a jump so if he falls into you he can do a rising Bair, you can't shield grab that either.
Fireball isn't really a huge threat of camping, Lucario can beat it out with FCAS at higher %. Fair can beat it out, etc.
The goal is to space and keep him out, if he gets it, it's gonna get really messy. Jab>UpB works hardcore on Lucario, be very very careful when he gets it, if he gets too close no DI will save you from the combo, if you have some distance you have a better shot to PS the UpB. Luigi's will use more Jab Dthrow if they can't kill with UpB yet since it set-ups with Uair and Utilt strings.
I'll post more later.