Level 55 is the max level, if you would like to continue ranking up, I suggest you enter Prestige Mode. This can be found under the Barracks. Note: You will have to start all over again at level 1, all your weapons, lethal, and tactical equipment will be locked until you unlock it again, weapon attachments and camos, however, stay.
No, you have to prestige to unlock more. Items you unlock through unlock tokens will stay unlocked through prestige, but you still have to rank up to get them.