Hello and welcome to the forum. The GTX Limited is an expensive beast. I watched a review of it lately on Youtube and it is the king of the Sea-Doo! I can answer a few of your questions.
Insurance: you must get a good maritime insurance for your new ski (responsibility and damage). I don't know the cost in the USA but here, I am in the $350.00 yearly range for a much less expensive ski (a simple GTI 2018).
Warranty: I got lucky last year with my new ski as BRP gave me two years of warranty instead of one. At purchase, you are offered an extended warranty at the dealer. In your case, I would make sure I have at least two years (and even three). Unfortunately, these supercharged machines are more prone to failures/issues than more basic skis.
Maintenance: as a rule and to avoid issues, I am having the maintenance done by the dealer until the warranty is over. Then I am planning to do it by myself. You will need a cylinder kit to change the oil as well as a few tools. If you need to winterize your ski, you will also need a kit for that.
Do's and don't: I am not sure if your burn in period will be computer managed (depends on models) but follow exactly to the letter what your manual says. Start by not speeding for the first five hours and vary your speed frequently. Then go easy on it up to 10 hours. At 10 hours, you will be OK. Let it also warm up a few minutes before riding. Open the seat frequently in the first few hours and inspect the hull for anything abnormal (oil, coolant, water). Never ride in less than 3 feet of water (idle at 3 feet is OK). Also, if you want to keep a nice finish to the bottom of your ski, never beach it. Buy yourself an anchor (plenty of small models available). I followed a friend's recommendation years ago: first, attach the anchor to medium chain (same length of your ski) and then to some sinking marine rope (same length as your ski as well). Basically I bought the anchor and replaced the existing cheap rope. That way your anchor will remain firmly at the bottom unless waves and wind) are really big/strong. And don't flip your ski! People think its cool but it is not so cool because your hull will get dirty fast. Also if you are in saltwater, you will have to flush the water cooled portion (muffler) after every ride with the garden hose. Never turn on the hose before starting the engine and always turn off the hose before stopping the engine. Never let engine run for more than a minute, even with the hose. If your engine got wet, there are some sprays to repeal salt on the engine. I live in a clean and pure freshwater lake so I am less familiar with this step.
Boat lift: if you have the room a Sea-Doo lift is always a good solution. Mine is floating because I can't install a lift where I am (because it freezes hard where I live and I am docked against a cliff). There are also some floating mats that represent a good alternative (I may get one one day).
And have fun!
