AI trading depends on a number of factors. First of all, yes, a hostile AI will be less likely to trade. And there's lots of ways to make an AI hostile (settling cities next to it after it asked you to stop, having declared war on it in the past, competing for wonders or city-states, etc.). Secondly, different AI leaders have different default personalities (unless you change this in advanced settings). So even if a particular AI is not hostile, it still may not trade with you (Harald of Denmark rarely seems to trade with me).
For your other question, a lot depends on the strategy you went with. If you only built a few cities and focused on building lots of wonders in them, trying to go for cultural victory, then by late game you may have to wait to pick up technologies to build more wonders and may just click through 10 turns at a time (though with a little planning you can avoid having to do this much of the time). On the other hand, if you decided to go for a conquest victory, you'll end up constantly moving units around, deciding what units to build, etc.
If you want to win by turtling up and going with science or culture victories, that's fine, but don't expect as much excitement in the late-game since these victory types require a lot of planning and generally are decided by the end of the mid-game.
If you want to have more to do in the later turns, go with a military victory strategy. There'll be a lot to do, even if you can see you're obviously going to win or lose, since you'll have to marshal your units around the map until the last enemy capital is yours (or until you've lost your own).
