First, welcome back! I too am a recent returnee and am having a blast. I'm going to assume you know about the essential NRAAS mods but if you're not make sure you ask someone about them. I only use a very small few of them but I wouldn't play without them.
As for challenges, I'm not particularly into those myself so I'm not the one to answer but what has brought a whole new aspect to my returning game play is using my actual playing family to tell a story and then sharing it on the
What happened in your sims 3 game today thread. I'm considering starting a story blog using the blog we get through TS3, we will see :) But it's definitely opened up a whole new reason and way to play for me :)