I'm a pretty recent Luigi main myself, but I've learned a lot about him in that time. In my experience and also based on what I've seen from experienced Luigis, there is no such thing as wavedashing too fast. There is such a thing as wavedashing to recklessly and predictably though when it comes to using it for approaches. Stuff like using it out of a dashdance is an example of one way to make it less predictable. If you want something to study off of, find some videos of Abate, Vudujin, or Eddy Mexico playing, imo they are three best Luigis in the world, just watching them (and listening to the commentators) can teach you more than me talking to you. As far as what tech to practice, I feel like a great place to start is practicing wavelanding until you can move around the stage freely and confidently with only a very occasional error. This is the first thing I practiced when I started maining Luigi and it made doing literally everything that I would want to do during a match easier on account of feeling more able to quickly and smoothly move around. Do this on every competitive stage (besides FD cuz ya know, no platforms.) Another thing (if you cant do it already) is to be able to short hop without fail at any given moment. Being able to short hop is necessary to basically anything in competitive play, especially with a character as floaty as Luigi and with such a high jump. As for matchups I can't tell you any details because I am still very much learning them myself. I can tell you though that Marth is hard to approach (no matter what character you're playing) so you have to get creative and mix things up to actually get combos going on him. Spacies are spacies, they suck to deal with no matter your character, it's really just as matter of being careful and learning how to fight them from experience. Sheik is Luigi's worst nightmare, you have to fight Sheik beyond tentatively and know at all times that she has the power to rip you to pieces in seconds. It is a doable matchup, though, you just need to be very very smart about how you play against her, I saw a Luigi 3 stock a Sheik at APEX, but I've also seen Sheiks make Luigis look like the worst player ever, it's all about how you go about it. Fortunately, there are some very knowledgeable members on the Luigi board that know 10 times as much as I do, maybe more. If any of them comment, they can tell you way more than I can.
