My two cents, start by getting a really good vise. Unless it breaks, your vise will last you, basically, forever so get a good one right from the start because a bad one will frustrate the heck out of you and make the job a lot more difficult than it needs to be. Anyone who's ever used a crappy vise then had a good one, knows what I'm talking about. A vise, like the one in this link, with adjustable end supports with built in clamps that hold the ski tight while you're doing side edge work are great to use. This is a pretty good price too.
For a first year U12 you shouldn't need more than a couple brushes. Stiff nylon and a medium bronze should be all you need to start out. You'll add more brushes as the years go on. Couple plexi scrapers. Three degree side edge bevel guide. File with at least 16tpcm. When you are starting out, it's better to have a file with more tpcm. Get a gummi stone, the Swix red is a good universal one. Down the road you'll need something to pull the sidewall back so a panzer file will be in your future but you shouldn't need one right away. Down the road if you want to spring for a sidewall planer feel free but a panzer file is very usefull and inexpensive item to have. A 200 grit diamond stone should get you started but you'll add more down the road. Use your diamond stones wet, they'll last longer if you do. Roll of fiberlene and a can of Swix glide wax cleaner. Opinions on this will vary but I nearly never hot scrape. I use Swix glide wax cleaner, notice I said wax cleaner not wax remover, instead of hot scraping and it does a great job. I'd suggest you use a good multi temp universal wax, something like Dominator Zoom or Zoom with graphite. Almost forgot, you'll want to get yourself a small spring clamp too.
Most importantly, make your ski tuning life easy and stress free by staying away from any of the trick go fast stuff. There will be plenty of time for that stuff later and if you don't really know what you're doing with a lot of that stuff, like many ski tuner parents, you're just spending more money but with no benefit. Get the most out of what you have before you move on to something else.