We realized as we were making the chocolate that we weren't sure when or how to add lecithin. This is where I found it. When do you think is best? http://www.thechocolatelife.com/forum/topics/at-what-stage-to-add-lecithin And Is it possible or how is it possible to add flavor oils to chocolate? And when does that happen?
Being a lazy sod (LOL), I add it to my cocoa butter at the beginning. Part of the reason also stems from the fact that I was not noticing a radical viscosity reduction when I added it later. As many point out, it's a matter of your process. I'm a big fan of 'don't fix it if it isn't broken' and much of my chocolate I bake with. And it 100% behaves better, truly lending it's emulsification properties at that stage. I add it to most since I'm in both a humid climate and mix it with water based ingredients once I'm done taste testing. And when I didn't have it in the chocolate I would often get oil breaks.
There are some good points people make though. With it in, you may bind water that would normally evaporate. But if it does not give you trouble, then why fix it? Also, (per the thread mentioned) it does act as an emulsifier…just with ingredients you don’t expect. Most people think of oil and water, but having two functional groups (a positive and negative if you like to think of it that way), allows it to form ‘bubble’ encapsulations called micelles, but instead of water being in them, they have a sugar molecule in the center and triglycerides (the cocoa butter) on the outside. In a way it is ‘removing’ some of the free solids in the chocolate, and the result is a more fluid, less viscous chocolate. So, it IS an emulsifier. Just not a water emulsifier.
You can certainly add flavored oil. Since you are adding it for it's flavor, I would personally add it at the last 1/2 or so of refining. Just enough to incorporate without driving off flavors And two words of warning. Not all 'essential oils' are oils. Hell, most aren't. They are ketones and aldehydes. But those will still play nice with chocolate. Most of the time. They just need to be lipid soluble. That ‘most’ back there is key. Some can seize chocolate, so test them first on a small amount of chocolate. Second is that some can inhibit tempering. And only trial and error will reveal that.
I hope that helps.