For the ranks, I think each rank could have multiple levels. This gives you a small goal (levels) and a large goal (ranks).
For instance, the lowest rank might have 5 levels. Then when you lvl up again, you go to the new rank. Then that rank might need 10 levels before you get the next rank, and so on.
For instance, the lowest rank might have 5 levels. Then when you lvl up again, you go to the new rank. Then that rank might need 10 levels before you get the next rank, and so on.