I have given myself the B-12 injection, I used a very small syringe,but, it was not an insulin syringe. An insulin syringe makes it pretty difficult to get the solution out, a slightly larger one is better.
As to where to inject, the top of the thigh is best. There are some videos on You tube that actually show you how to give the injection, also, the doctors nurse should be able to help.
I would not recommend using an insulin syringe unless u have before. I would defiantly say in the buttocks or the top of the thigh where every the most fat is. Do some really deep research before making a choice.