Re: What else do you need?? Extra rotary blades for one thing. I have a suggestion for you. Look through catalogs ... ones you get in the mail or go on-line to all the places that sell quilting notions. You might get ideas of your needs from seeing what is available. There should be a detailed description of the purpose of each item. I must confess that I have bought a lot of things over the years that I have yet to use and a few things that I've tried but don't like.
Your other question about how to secure your quilt sandwich ... the answer somewhat depends on what sort of area you have available in which to lay out the layers and put them together. A lot of people put their layers on the floor and work on their hands and knees -- in that case, I think kneepads would be helpful. I have a 1/2-inch thick sheet of plywood quite high up on sawhorses so I don't have to bend over far. I'm able to smooth and pull the 3 layers taut, clip them to the plywood and then pin them together with quilter's safety pins. It works exactly right for me, but there's a lot of different ways to go.