I get my flavorings and glycerine on the Lorannoils website, the super flavorings for candies. I do try to stay away from oily flavors, however if you do get one, you can normally let it set for a few days, and pipette out most of the oil so it wont interfere with the atty, and it works well. Liquid nicotine you can get from a lot of different places, I currently am mixing with 100mg from xtremevaping, and its pretty nice.
If you end up using a really strong nicotine -- just remember, a little bit goes a super long way!!! I mean like 5-7 drops per 3ml! Also, with lorann flavorings, they do vary. Best thing I can tell you is to make a little batch, try it, make your tweaks to it, and get used to mixing by taste. Just dont keep adding more and more nic unless you are going to add other stuff too!! hehe, hope that helps, good luck!!
oh and Wiltons works pretty well, but for me it oils up and I end up soaking it for a little bit, and taking the oil out. U can get big ole packs with 4 flavors in them for 5 dollars, and it gives quite a bit...but yes it does work pretty well