The developers changed the battle score to experience gained ratio to help people gain more resources (such as crystals and supplies) before ranking up so they can meet their equipment requirements at that rank.
So basically, you rank up slower than before, as actions like killing don't give as much exp as before. 
Premium does increase your exp gained per kill (and other actions) but due to the decrease mentioned above, it finally equates approximately to the battle score you earn.

As long as your Overdrive is active, any kills or captures you do won't contribute to OD recharge.

Kits in the Shop showcase rotate every 12 hours. Usually a few are available for crystals and you might get lucky enough to get your preferred combo (out of the total 98 combos) for crystals, but yeah, it's not of much use if you aren't extremely patient and have restricted choices of kits.
But hey, if you have a suggestion regarding crystal-kits rotation (a not "Tanki is DeAd" one, constructive criticism works better), you can post it in the ideas and suggestions section. I guess we all will welcome one, except Maf (he'll probably decline ?).

You will get the M0 (or Mk1) modifications of the turrets and hulls that you don't own right now.

Your Profile may have been duplicated after the Forum update. Contact @Maf via Forum PM to merge both accounts.