Greetings man, I'll recommend you to create and account and login to battlelog since that's where you will see all the things that you need to do to unlock weapons, perks and level up the rank.
Some weapons for example are unlocked by completing singleplayer, others by leveling the same type of weapons, the perks are unlocked by battlepack and by kills etc, there's so much content in the game to unlock that you will keep a better track by checking Battlelog.
Anytime man, yea Battlefield 4's Battlelog will be linked to your Battlefield 3 profile. Just boot up the game on the system that you will be playing and wait until you get to the main menu. Chose customize my soldier etc, then just exit the game and login to your Battlelog account and you will see your character's stats on BF4, BF3 soldier's stat will be displayed below your profile and you can check either one of them at any time.