Could you elaborate on this? I'm not sure I follow.
In Melee, you can't change your controls. The ability to do so was added in Brawl (and therefore in Project M). By changing other buttons to use your specials (e.g. many people change all of their dpad buttons to special instead of taunt), you can press multiple buttons on your controller, even using both of your hands to mash, therefore registering more inputs with less effort.
So it can't be meteor cancelled?
Correct.
So it can be used semi-like the captain falcon uair?
Semi-like that, I suppose. Though only to a very small extent, due to Luigi's much lower range, poor air speed, and slow fall speed. Luigi just can't move through the air fast enough to carry opponents across the stage like Captain Falcon can. I guess it's more of a vertical combo move while Falcon's is more horizontal.
Will it do a regular missle if i store it (i.e. at the time i charged it) or will i start floating and be forced to downb or missle again?
It will do a regular missile.
Not really a question just more confused on wording. You say "somehow" but at the same time you say that they link properly (i.e. if the first/n-1th hit connects, it will continue to the nth hit with no ability to get out of it). So I guess my question is what do you mean by "if you somehow manage to connect all hits", it sort of contradicts with "links properly".
That's fair. I suppose I exaggerated and should have said "links better". It generally links properly at lower percents, but it has some knockback scaling so it stops connecting at a certain point. It's also very punishable if it doesn't connect, so it generally goes unused, even if it is heavily improved from Melee. There are also more frames between each punch as the move goes on, so the first few connecting doesn't mean they all will. Fortunately the move is more difficult to SDI out of due to SDI and hitlag multipliers.
Minor correction: The hip hitbox was actually in Melee. I'll change my original list of changes to reflect that. I also forgot to mention that Luigi's missile can sweetspot the ledge. Mastery of that skill definitely helps his recovery.