The Qubes can be used in the GO cutter. Depending on which size qube you select, you may need the GO big. The Accuquilt page for that size qube will tell you machine compatibility.
https://www.accuquilt.com/go-cutter-...hoCn0sQAvD_BwE
If you go to one of the pages for a Qube, they list all the dies included in the set, mostly squares and triangles. If you already have some squares and triangles, you might be farther ahead by purchasing the rest of the dies individually. The qubes are nice as they have gathered the dies that work together, however, because they all fit in that cute box, many of the dies only cut one of the shape. Often (but not always) the stand alone die for that shape will cut multiples. You would have to add up the prices of the individual dies to see if there's a price break for purchasing the set. You can also purchase the book with the block patterns.
https://www.amazon.com/Quilt-Day-Mat...+in+a+day+qube
As far as the size, that is an individual choice. Do you like big blocks for a quick quilt, or smaller blocks?