Here's my assessment of the beginner-potential for each of these pieces. The students can choose to make one of these designs (#1 would have to be simplified) or come up with something completely their own. Simplicity is key.
#1 - Design too complex; cutting too precise. However, it illustrates different andamenti, nice texture, and could be simplified.
#2 - Suitable for beginner. A beginner's would actually be better, I think, as it would be more loose and the lines would have more movement. (I tried to make the lines a little crooked, but mostly failed.) Nice variety of materials, plenty of straight cutting, no angles. Could easily be made more challenging.
#3 - Suitable for an ambitious beginner. A little more demanding than #2 and #4, but still easier than it looks. The design/style is very forgiving and could allow for looser cuts. The surface texture is very dynamic. The porcelain outline of the half-circle and the 3 extended lines could be left out as they are not necessary.
#4 - The most beginner-ish of the group. Easy to work in squares and let the widths of the material guide the interiors. Could easily up the challenge by making the geometric interiors more intricate. Really interesting geometric texture.