What you'll find is there are a wide range of skill levels from the world class (MKU division 1) to the fresh competitive players (MKU division 15 as of last season). As you play more your team may move up the ladder or you transfer into a new team.
It's important to recognize that you can only be in a SINGLE team for each category (150cc, 200cc, MKTour) at any one time. If you transfer to a new team, you can't play for that team until a new tournament starts. There are new tournaments starting periodically, maybe a dozen a year for 150cc team mode, and you don't have to play in every match. Usually the team leaders ("captains") will select the starting lineups for the team before a tournament match (6 players per team at a time). You'll find LOADS of opportunities to play practice matches ("scrims") against other teams outside of official tournaments. This is one of the best ways to develop skill and team chemistry.
Teams are more than a group that plays together. They tend to get to know each other as friends and (hopefully) support each other. That being said, it's common for players to leave a team for a new one, although team loyalty is valued by many.
As for gameplay, most players do not have 99999VR. The way the VR system works is it is biased upwards, so that you gain more than you lose even if you consistently place in the very middle of the room. So this makes VR an indicator of how much you play in the Worldwide/Regional modes and not skill per se.
There are a lot of techniques top players use. Holding stars/bullet bills/ghosts to dodge an upcoming shock (lightning bolt) and run away is a crucial one. Playing it slow on lap 1 to grab power items heading towards the end of the race (termed "bagging") is also common, but not every player will do this and it is only effective on certain tracks. Usually players will take a blue shell hit or try to dodge it, but it's not unheard of to drop back especially if you're right in front of an opponent. It's all part of the competitive strategy.
Discord is crucial to have for communication. In fact, you're required to provide it when signing up on our registry. It's important to at least listen in to the voice chat during a match, although it's much preferred if you can speak. I highly recommend getting set up on Discord. The Nintendo chat app is not used.
Finally, a couple last extra points. You may wonder why we don't use the in game tournament feature, or the team setting in-game. The reason is they are anti-competitive, for various reasons. Tournament mode in game first of all only shows the top 20 players, and also there are no good options to set it up for a truly fair and even tournament. For that reason players here play in friend lobbies. Also, the team setting in game makes certain items too powerful. You could use a shock/lightning lap 3 and EVERYONE on your team dodges, destroying the opponent. It makes for a less enjoyable experience. Having players on your team coordinate dodge items with shocks will add strategy and technique to the game. Same can be said for other items as well.
Last point: Don't be afraid of the players who are "better" than you. They were once new to the game just as you are. As long as you have a healthy mindset and open to constructive criticism on your playstyle, you are bound to improve too, with time. And finally, if you have any concerns, don't hesitate to ask a site moderator on Discord. There's always some available and we're there to make this site great.
Thanks and have fun!