I would do the dress in many layers, then attach them together for simplicity of dressing once you figure out what can go on what permanently. Likely all the skirt layers can attach to each other at the waist.
I Did (half of a) Mage tier 5 once upon a time, so I totally get the context
the longest skirt layer and the medium layer both have the wide gold edging, It's big enough I'd do strips of a contrasting fabric on the bias instead of trying to use ribbon or anything like that. Clearly this trim is 'fancy' and that works to your advantage because you don't need a whole lot of said fancy gold fabric to make the gown really stand out, one yard of something pricey & elegant should be more than enough. I would NOT use a satin for the blues. I'd look for something with good drape and possibly even a subtle print to give it more visual interest. My mage gown was a rayon dress fabric.
Don't let bias cutting/ sewing scare you, this is a good type of thing to learn it on.