I'm doing a Wedding cake and it's going to be covered in BC icing. The bride wants to put fake silk flowers on it....I've never used anything non-edible on my cakes before. How should I approach this.....

Wash the flowers first and bag them, them just stick them in the cake. I prefer working with silk for that reason - washing them first.

So it is okay to put the stem in the cake? Sorry if the question sounds stupid, it's just I thought I read somewhere else that the stem of silk flowers could cause an issue especially with the metal...

if you're nervous about plunging the whole stem into the cake, then here's what I do/did with most of my silks .... I cut the stems off close to the head and glue the flowers in place with a blop of icing. I just didn't like the idea of a bunch of holes in my cake. that's the only reason I ever did it this way. You'll be fine.

Depending on the arrangement and the width of the wires, you may be able to stick them in one of those plastic flower picks (Wilton) and then insert them into the cake. I've done that before, and it looked just fine. I did have to build up the wire stem with floral tape to get it to fit right into the pick, though.