Stats don't directly affect rank, no matter how impressive they may be. Rank depends on score. Crystals give 20 score, and units also give power which translates into score.
25 workers - 1 power
10 infantry - 1 power
10 vehicles - 2 power
10 tanks - 3 power
For a build, you should only build one chassis. Here's how I build my squads
Infantry - 10 armor, 10 damage and 10 range in each squad
Vehicles - 5 armor, 5 damage and 5 range for each squad
Tanks - 3 armor, 3 damage and 4 range for each squad
If you need to know anything else feel free to ask.