Objects for number arrays like this:
1_xxxx_primarydigits_4: has 4 quads mapped with textures called Primarynumber_0 through 3 from left to right ( so the 0 is in the highest digit spot )
1_xxxx_primarydigits_5: has 5 quads and as above. It's in the same physical position as the above
1_xxxx_primarydigits_6: has 6 quads... you can see the pattern.
Enter a 4 digit number and the 4 quad model is used, enter a 6 digit and the 6 quad one is used. All there is to it.
I've generally called the materials whatever I feel like ( albeit prefixing with decal_ ), despite being told not to. The texture map names are important though.