Game 1: Good choice to play keep away with the missile game. That Luigi player isn't very good at all, and his movement was piss poor. Take advantage of that as much as possible. If you ever come across a better Luigi player, one of the biggest things in your mind should be making sure that ************ doesn't get on top of you. Because you will have a bad time.
As far as deciding to go with ice mode, I'm unsure of which beam works best in this MU. Whenever I play with Sago, I feel like he struggles with all the multi-hits of plasma beam, and it racks up damage super easy, and missiles play a bigger role in hindering his movement. Fire missiles are better against movement heavy/down b heavy Luigi players, from what I've observed. Of course, you've got your standard ice stuff that kills early, but I feel like both beams are effective dependent upon the play style of the Luigi.
Game 2: Go to around 6:50 on the time stamp. That bomb you do there, is really poorly thought out. Bombing out of hitstun is super amazing, but you have to know where to go after you drop the bomb. You had a juicy platform sitting right there on your left, and you drifted instead to the right, and directly on top of Luigi. Furthermore, you put yourself in a less than stellar position by sacrificing all stage control and moving to the ledge after taking the stock. Not all characters can just do that. Sheik can do it because Sheik thrives at the ledge. Samus isn't godlike at the ledge, she likes the center of the stage a lot more. If you're trying to stall out the invincibility, you can try using crawl and boost ball to keep yourself mobile and hard to lock down. Just stay on the stage.
You seemed to be looking for a set up to charge shot on that last charge last stock. In a deficit like that, especially at lower/intermediate levels of play, it's not really a bad idea to just dump the shot out and see what your opponent does. Sometimes people freeze up and eat a dumb charge. Most of the time, they pick a bad option and you can cover it. Also, he started grabbing more towards the end of the game, but he wasn't grabbing nearly enough. In that case, you should just hang out in shield and let him poorly attack your shield. UpB isn't a good option OoS against the Weej, though. Nair is far better, and it can lead to stuff at high-mid percents.
Game 3: RIght off the bat. . . hold on to your damn double jump. You're up against one of the most ferocious edge guarding characters in the world, and if you don't have your jump, you're gonna struggle. Stop relying so much on missiles as a whole, but especially in this MU. You have to play the game as well, you can't just let them do all the work. Kirby has good aerial mobility, and his aerials are able to break your missiles, so he can approach through them safely. Instead, you need to focus on strong ground movement and getting him above you where you can hit him with the tips of upair or even upsmash. Kirby on a platform is just asking to eat some ice. Once you hit him once, establish positional control and work on a charge shot. Charge shots take up a lot of space and he can't beat them with aerials. Once you've got a charge on line, you can throw some missiles down range to try and burn his jumps, thus guaranteeing a charge shot to hit. Even if you don't land the charge, all you have to do is win another single exchange and charge up again.
If you ever find yourself fighting Kirby on a triangle platform layout, just let him circle camp you. You'll be able to land enough upairs and upsmashes to establish a lead.
Don't over extend for an edge guard, especially against multi-jump characters. If you're gonna go for Kirby, be above him and go for dair, otherwise just set up for an edge guard.
So much jumping in the neutral. So little space between you and Kirby when you jump. So much wrong with this idea. Stay on the ground, unless your going to a platform for movement. Back to the idea of bombing out of hitstun, you can't do it against multijumps, because they dgaf about your bombs. They just hit you while you're in helpless. Just DI out and get away, take whatever damage you must, but hold your DJ and try to move to a safe position.
Separate yourself more. Max ftilt range should be where you're fighting. Kirby struggles more when you outspace him. If you come right in on him and jab2 his shield, you let him win the exchange 10 times out of 10. If you're in a position where you're in the neutral and find yourself above Kirby, FF dair can be incredibly effective, especially if you land behind them. Those missile dash attacks you're doing that KB stack can be missile upsmashes, and those kill. Try it out every now and again, works wonders against floaties.
Overall: Calm down with the missile play and focus on the rest of your neutral. Your ground game is lacking, and you seem to favor an aerial style when not shooting missiles, but your spacing is sloppy and you're impatient with your option selections. Aggression works sometimes, but you can't do it to Luigi because he gets comboed even less than Samus does, and Kirby will eventually just jump away and win the aerial game. Work smart, not hard. Your movement also needs work in general. Again, the missile game is fine, but your wavelands and wavedashes aren't always crisp and could just use some polishing. It'll come with practice. Your ledge play is also a bit slow (as is mine, I need to work on it a lot), so work on making every frame of invincibility count.