You can do 5x5 characters, but 5x7 looks better and 5x9 if you want lower case. (WxH)
You need at least 5 characters wide to be useable...
If you want better than dot matrix fonts, you are going to need more vertical and horizontal pixels.
Mine was 8x30 and I never touched the bottom row... It was also a lot more work than I expected.
If you want to map video to it, you need to plan 4x3 increments or the video will be stretched to fit...
In LSP, you can drop a video effect on a layer. You just define the layer to include the matrix and then make your video. I forget the parameters that I used last year for the video, but I'm hoping a new version of LSP will be more forgiving this year... I could only drop about 30 seconds at a time and topped out at about 7 videos...
RM