If they are around the same size and age either a red or a B&W should be find togeather. Later you'll have to worry when breeding season comes around though, unless thats the intended goal. As for the furture cage size, 8x4x4 is fine but as far as reptiles go, bigger is always better for cages.
-----
Leo Gex
1.0 Giants
0.1 Red strip/hypo
1.0 Patternless
0.2 Normals
Others:
1.0 Giant plated lizard
1.0 Blue Tegu
1.1 dogs
2:0 chinchillas