Belegarth

Before I dive head first into my newest feast garb attempt, I just want to make sure that I have order of operations correct, so I don't regret doing it backasswards.

If I am wanting to embroider something on say a cuff or collar that I intend to back with some interlacing should I be doing the embroidery before I do the interfacing?

You can do it either way. If you want to be able to cover up the backing threads and you're going to sew the interfacing down, then do the embroidery first. Structurally, there is no difference. Just be careful that the stitching of the interfacing doesn't go over your embroidery.