I use the 2.5 strips, 2.5 squares, and 2.5 triangles the most.
I bought a couple of sets - drunkard's path and hunter's star only because I think it may be easier to make them, especially the drunkard's path.
I had no clue what to buy at first but maybe start with some basics and then go from there.
I don't know anything about the cube sets but others will be able to tell you about them.
Many on this forum have this system so you'll probably get a lot of info
I hope this helps!