1- His biggest strength is probably his edgeguarding game. The air speed buff as well as range buffs to all his aerials further compound this. If there's one thing you should never do as a Meta Knight main, it's let your opponent get back to the ledge for free. His disadvantage state is also amazing because Mach Tornado is very fast with a lingering hitbox and Dimensional Cape (no attack) is very ambiguous in terms of where you'll go, so using these two moves in tandem will help you get out of bad situations pretty effectively. Oh, and he's also a pretty good combo character.
2- Unless you get a raw f-smash, back-air, or Dimension Cape read, Meta Knight can really struggle to kill. Up-throw doesn't kill until like 200% and back-throw won't kill at the ledge until about 160% if it's fresh, which it usually isn't. Shuttle Loop's kill power was also nerfed from Smash 4, so it's way less reliable to use OoS or as a surprise attack and kill confirming into it is more difficult. Another weakness is that his neutral is pretty linear. It's actually a bit less linear in Ultimate compared to Smash 4 because SH down-air is better due to the range buff and being able to use tilts out of a dash helped out Meta Knight more than most, but it's still one of his weaker points.
3- Similar to Smash 4, you'll want to look for openings to land a grab or dash attack. As I mentioned before, SH down-air is also very good, namely at stuffing approaches or poking the enemy's shield if you retreat with it. Down-tilt is tied for the fastest down-tilt in the game at frame 3, making it a safe poke and his best tilt out of a dash. Forward-tilt got a huge quality of life buff from Smash 4, making it a great way to punish most attacks out of shield. Aside from those things, his other aerials besides up-air can be decent in the neutral as long as you aren't being too obvious with them because they're pretty easy to punish if your opponent knows what they're doing.
4- If they don't DI down, down-throw will combo into up-airs against most characters at low percents. If they do DI down, you can combo into running up-smash or dash attack. Another good early % combo is early hit dash attack > up-tilt > up-air > back-air/forward-air/neutral-air/more up-airs depending on how they DI. You can also get a landing neutral-air and that will combo into the dash attack or grab.
5- Forward-smash is his best smash attack because it has very little end lag for how strong it is. Down-smash is very weak, but it's the fastest down-smash in the game at frame 4, so it has its uses in killing. Up-smash is good if you can chase the opponent's landing. If they aren't respecting Shuttle Loop, you can catch them in the air with it and it will kill decently well (it also seems like the first hit leads into the second hit much more reliably in this game). Dash attack's knockback was buffed from Smash 4, hindering its combo potential a bit, but allowing it to serve as a quick kill option at roughly 170%. Unlike in Smash 4, forward-tilt actually has good kill power at the ledge. Back-air has insanely high KBG, making it Meta Knight's strongest aerial for killing and neutral-air is also pretty good if you land the sweetspot. Finally, while punishable, Dimensional Cape can kill quite early if you get the read.
6- While most of Meta Knight's advanced combos likely haven't yet been discovered, here's a pretty interesting one utilizing the new attack cancel technique. I recommend watching the entire video to understand how to perform the combo properly.
https://www.youtube.com/watch?v=v1kjQtMaPkE&t=9m6s
7- It may be tempting to dash attack out of down-tilt at low percents, but it's not true unless the opponent trips. You'll have to wait until mid percents (about 50%) before it starts comboing because at that point, it'll start sending the opponent off the ground. Landing bair and landing fair is a lot better for comboing in this game compared to Smash 4 because of the landing lag buff, so you can follow up with down-tilt, forward-tilt, grab, etc. Finally, I'd like to say that Battlefield is Meta Knight's best stage in my opinion because the platforms really help his up-air ladder combos and they also allow up-throw to actually kill at reasonable percents.
I'm not the best Meta Knight player (as evident by my profile), so there's probably a bunch of stuff I missed that other people could add, but these are my two cents.