Gilad,
Please contribute your examples - some questions might help as well.
Also, please take note of the existing functionality in Maxima such as
"C:/PROGRA~1/MAXIMA~1.1-1/share/maxima/5.31.1-1/share/physics/units.mac"
[or the equivalent path on your machine of course]
This is a very simple file of units.
Much more substantial is load("unit"); but this is very slow to load.
Also, there is an "ezunits" package. I've not had time (or need) to investigate these properly, but it would be sensible for you to do so. I expect you will find much that you need, and it would be a shame to have yet more Maxima commands which do substantially the same thing.
If you need to load a package in your own version of Maxima (for test or implementation) you can add a line to
...\moodle\question\type\stack\stack\maxima\stackmaxima.mac
This can't be done per-question or by the teacher - it would be a huge security risk.
Please let me know how you get on.
Chris