Tournaments are really conventions that happen to be running a bracket. You should expect your time in that bracket to be short-lived, especially if it's your first time. So rather than give you any advice for the bracket itself, I'll tell you everything else you should know about having a good time at a major.
Bring a water bottle. Stay hydrated. This is the most important thing. Seriously.
I don't know if this will really be viable for 8-player Splatoon, but if you play any other 1v1 games, try to get as many casual matches in as you can. Because again, you'll probably be out of the bracket pretty quickly, you don't want that 0-2 to be the only games you played all weekend. There will be plenty of open setups not in use for bracket, anyone is free to hop on. If you see someone in Training Mode, they're probably waiting for anyone to come join them. And before/after bracket, all the setups will of course be free. There may even be a dedicated Free Play/Bring Your Own Console area. Just be courteous if there aren't a lot of open setups, don't hog it for too long if you see others look like they're waiting for a turn.
Speaking of other games, enter as many brackets as you'd like. I don't know what all LTC will have, but keep an eye for out for side events. If you see any game you have even a passing interest in, you'll make a TO very happy to give them a +1. Even if you think you don't know the game very well, you might be surprised to find out half the bracket doesn't either. I ran a 10-man bracket once and it was a wonderful time that I really want to do again someday.
There'll be plenty of other activities that aren't brackets too. I've never been to LTC or the Kalahari Resort, but I know they've got a waterpark so that's gotta be the attraction to not miss. Majors will almost always have a lot of arcade cabinets, check those out. And there will be groups doing their own thing somewhere. One of my hobbies is Riichi Mahjong, and I have a few friends who'll bring their sets to FGC majors. Once I'm out of the bracket, I'll meet up with them to play for a while.
Figure out dinner plans. I assume you're going with a team, so the obvious thing to do is reach out to them and see if they wanna head out together after hours. If you're lucky you might be able to make connections with someone local, maybe even someone with a car.
Hotel room gaming is a thing too. At Combo Breaker last year I brought some friends back for a few rounds of Ultimate Chicken Horse on my Steam Deck setup before we called it a night.
Speaking of Steam Deck, portable setups are a godsend. You'll obviously be bringing your Switch for Splatoon, you could consider getting a third-party dock that doesn't cover the screen and then you can set it up anywhere, don't even need a monitor. Laptops are great too.
Bring spending money, there's gonna be a lot of artists and vendors selling all kinds of souvenirs. Get yourself some nice stuff with your favorite Scrimblo on it.