Definitely don't buy a ruler shorter than 24" long as you won't be able to cut wof (width of fabric) strips easily with a shorter one - ask me what I bought as my first ruler - why 18" of course........ Same for a cutting mat.
Like you, I started from scratch and it is very tempting to buy everything at once, but take your time. The supplies aren't going anywhere and can probably be bought as you need them. Seam ripper, scissors and some quilting pins are mostly what you need for the moment. I hope you enjoy your class.
