Tomorrow I'm having a sushi party for my birthday!
I wouldn't get a kit, it's gonna be more expensive, just get sushi rice, nori, rice vinegar and fillings, then a bamboo mat and like the other poster said, make sure your knife is good and sharp.
We make the rice, mix vinegar with sugar (I would estimate 1/2c vinegar per cup dried rice, and 1/4c sugar per cup vinegar, it seriously makes it more delicious if you have the vinegar and sugar, much
more) and add it too the rice after it's cooked. I just pour it on and put the lid back on and let it absorb, then take the lid off and let it cool until it's pretty darn cool (it's better if you can wait, hot rice makes the nori bunch up and when it's cooler the grains stay more solid instead of getting squished). You could cool it by putting it into a bowl and stirring gently and fanning it and whatnot, but that's a lot of work.
For fillings we usually put avocado, mango, veganaise (Our Japanese friend got us started, I swear, we don't make this up, it's authentic!) green beans, asparagus, red pepper, cucumber. We've tried everything in our house, with varied success. Greens like spinach or sprouts make it harder to role (though sprouts do taste nice), we used to fry tempeh up and put that in, which is super but more work than we usually want to go through. Celery just isn't worth it. In our minds, if we have avocado and mango, we have sushi!
We've also mixed nutritional yeast with flax oil and put that in, it's very good.