Thx for your input. I appreacite. I plan to start progressively with 1 matrix... but I will buy the whole thing so I have to start planning.
I feel that I am not really at my place here : :-/ I might be too much newby for this community. I have more success with the same question at Sparkfun.
Sorry for all these newbies questions and thanks for the link, this will help me to understand.