Level 26 is the level cap and I believe you get 10 gems each time you level up so that would mean you could end up with a total of 160 gems by that time. As far as the premium weapon goes, the anti gravity blaster up2 is generally regarded as a better weapon although not all agree on this. Also you must consider how much the the upgrades will cost you as I am not sure if how much it costs to fully upgrade it. The dragon breath is a pretty solid choice and it has no additional upgrades. Finally if you take a look at my thread in the general discussion section (weapon damage trial) I compare the strength of these two weapons among many other weapons. Hope this helps.
