On the one hand I have been playing Civ-like games off and on since there was a Civ to play. But I have never really been that good at it. Nonetheless I have found that with all the default settings in my first game (as a Mezari) I have had no difficulty beating all of the challenges the quests have offered and although I have stayed in the lead from the beginning, and wandered into my neighbors' empires frequently, they haven't teamed up against me or decided to fight me individually. The game's description of "normal" suggested that it would give me a challenge. Is that not right? If I cranked up the AI would it make them more powerful or just more aggressive against me? Or both? Or is there a certain point I haven't arrived at yet where the AI will decide I am too much of a threat and try to beat me?

You are at the point to download and install the Endless Legend Community Patch

I suggest trying Endless difficulty first.

Normal is very easy in this game - probably even with the community patch. If you are experienced I suggest starting with hard and the community patch (which overhauls the AI).

I take it the patch does not itself break anything and is up to date? Can you give me a link? 

A link has been posted above by Groo. I maintain the patch and you can always report bugs in the thread itself or the discord.