Darth Malgus as a 1st costume, to join the 501st, is not an easy feat, as this is not an easy costume to put on or to wear the whole day at a troop.
For the normal person, I would suggest an easier costume to start off with and then to try to make something at this difficulty level.
Approval is dependent on your local Czech Republic GMO/GML. You have to attain the right look, compared to official reference materials.
If your GML/GMO has any questions with your approval pics, they will submit them to us, and we will give our opinions.
The costume in the Video would be approvable yes, but most people in the 501st don't have a "team" to help them get dressed and put on makeup and prosthetic. It is unrealistic to have to show up several hours before the troop to start putting on the costume.
Pants, find an official LFL reference to support your look, and you are fine. I have seen black, and I have seen gray, so for the time being, either.
Materials for the armor is up to you, but it must look correct. It has to have a thickness to it, it has to look like hard armor. Lights and everything else seen must be included.
Find an official reference you are happy with, and make your costume look like the reference.
This costume is not an easy one to pull off the correct look. This costume is also quite expensive to pull off the correct look.
Not trying to discourage your interests, but many have started this costume and not seen it to the end, and then it was just a waste of time and money, and they never got into the 501st.
Many have attempted this costume, currently only 2 have an approved Darth Malgus in the 501st!