Ranks

Do I need to by all the lower ranks before I can buy the highest one unlocked?

nope, you can wait till whichever rank you want to start purchasing, but you will need to maintain the points required for that rank. ie: Sergeant requires for you to have 1450 points. To get this rank it requires 1450 points and 600 tokens. When you purchase, only the tokens are spent, you keep the points you earn. if you wait, and just purchase your first rank at Sergeant for example you will need to maintain your points to be 1450+, otherwise it will fall back to the the next highest rank that you PURCHASED, which in this example, back to a basic rank.

That actually makes much sense and is a clever mechanism.

Thanks.