Pressing Pleats, what I'm considering

[The Wizard of BC]

You can of course do what you are planning.
And from your description I think you are planning right. From the center of the top buckle up to the waistband the pleats should be the same width or flare outwards slightly.

If I may suggest - And this is exactly how we re-size a kilt - find a small piece of something like formica (Arborite here in Canada) or anything which will hold up under the heat of your iron.

Mark your pleats and then slide the formica into the pleat. It will form a pressing shield protecting the rest of the pleats and give you a nice sharp creases edge to the one you want.

Here is a pic showing the same idea being used to iron the pleats of a Cotton Kilt when the edges curl.