In my experience, your first year when you buy in will be the most expensive. If money is tight I would suggest spending where it matters (tools and safety). While the laser tools are convenient it’s not a necessity. Hopefully, you have or will make some connections at the track where you could borrow someone’s lasers. Another option is to look for used, they do come up from time to time.
Nice! When in doubt maybe add a bit of extra toe-out. Karts really hate being toe-in. Better to a be extra toe-out and scrub a bit of speed versus toe-in.
As others have mentioned in order of spending money in my opinion it should go best helmet you can afford, suit, gloves, shoes, necessary tools, then the fun “go faster” tools.
Rotax says just distilled water. You could run a small amount of an anti-freeze or water wetter to help with corrosion. It’s very easy to drain on the Rotax just by removing the lower hose so I do it pretty often.