Even if they don't have an army, they probebly still have a defence force of some kind to protect them selves.
They don't need to make anymore Gems, since they probebly have a very low death rate due to the fact that shattering is the only way to permanently kill a Gem. They only kept making new Gems because they were expanding there empire, which their not doing anymore.
Well, the Crystal Gems are all living proof that Gems are adaptable. (e.g. though Pearl wasn't made for fighting or engineering, she still manged to learn how to do it). Also, Gems can still do the jobs they were designed for if they want to, they just have the option of doing another job.
Well just have to see if anymore problems arise.