Going to build your own, or buy them pre spun? I would say 3mm is a good starting point. I have a few rda's that I like different id coils in, but 95% 2.5 or 3mm for me. Do you know what ohm you would like to target?Yes I meant what size coils would you recommend, this will be my first rda so I am just trying to learn as much as possible thank you for the advice