I'm a bassplayer and soundman. I have been on IEM since 2003. I started with Shure E3, then E5, then UE7 and have been using the JH13v2 for the past 2 years. I liked the UE, but with the JH (6 drivers), I run my monitor mix flat where I used to boost a bit at 80Hz and 2-4kHz. I started running stereo IEM mixes a few years ago and would not want to go back to mono. The trick with panning is to not hard pan anything. You want a natural feel, as if you didn't have IEM at all. Do not pan yourself. Pan the other musicians according to where they stand relative to you. How much you pan them is up to you. I start with 10:00 and 2:00 and go from there until I can hear the separation. Even if the drummer is right next to me, I pan the 3 toms and overhead mics while the kick and snare are straight up the middle.
I say to not hard pan anyone because of the following. When you are open ear, even if someone is standing to your right, you can still hear them with your left ear, albeit not as loud. You want to replicate the same "feeling" with the IEMs.
I noticed that I have been running my mix quieter since having gone stereo and can hear myself much better. The tone of everything in my mix has also improved with an increase in clarity (probably due to the removal of mud when everything is mashed up). As others have said, custom molds are the way to go as you need the seal for low end retention. They are also useful on planes, riding mower, motorcycle and while checking out youtube in bed while your s.o. is sleeping.