Very easy to link tickets from UT to MDE. Order the e-tickets and link the ticket number to your account. UT is great to work with. I have used them at least 10 times.
Don't spend the money on packing cubes. Go to the Dollar Store and get a few different size clothes storage bags. They work great and you can see what's in them.
The first week of June is generally "Gay Days". Crowds are lower. If you are offended by this, it is not the time to go. We went one year whenmy kids were 4, 6 an 8. They asked a few questions, but we got by it.
I called WDW today because I also have E-Tickets. I have linked them using the confirmation number to MDE. I also purchased magic bands thru WDW which I will link to MDE. The CM said that I still need to pick up the tickets at will call and link them to MDE. This puzzles me, but why take chances?
During that week crowds will be heavy and getting bigger each day. Wait times will be high. With that being said, it is a wonderful time of year to be at WDW. If you can go a week earlier, the crowds will be much lower and more manageable.