I only use plastic crates as my dogs much prefer them, and the only brand I trust is Vari Kennel (the dogs managed to break out of other brands somehow). The 200 Vari is what my friend with an adult Miniature Schnauzer uses, though as a puppy, she had the 100 for her. I'm not sure what the dimensions are for either size, but I'm sure if you looked it up online you'd be able to find out.
As far as other must-haves, you need to have good chew toys! My puppy couldn't live without her Kong or Nylabones. She chews on both all the time. She also has various stuffed squeaky toys too, but only for supervised play or else she tears them apart. Then of course you need a leash, collar, shampoo, stainless steel (or ceramic) bowls, etc. but those are pretty obvious.