All in all the concept works and looks great. Just needs a little refinement.

I'd opt for a wider belt with a kilt. Something between 1-3/4" and 2.5". I noticed in the Marine Corps League web store they have a square waist plate style buckle and belt for the 1-3/4" belts or you could look at Stillwaters belts and Marine Corps buckles.

The jacket does need to be tailored for wear with a kilt. It won't take a lot. Just shorten the length raise the pocket flaps an inch or so and add a sporran cutaway on the front. Several members have done this, as have I, and it can run between $30 and $60. This would turn the jacket into essentially a Crail jacket and give a much nicer look. Standard suit jackets are just too long to be worn with a kilt. The bottom of the jacket should fall just above or right at the widest part of your hips or where the pleats are not sewn down.

Personally, the red in the tartan and the red in the jacket, cover and flashes clash to my eye. Not a big deal but if going for a uniform appearance I think the reds should match. You might have better results with the Leatherneck tartan.

I'd also lean towards a simple black sporran. No need to get one with a bunch of nickel accents on it as it would only clash with the brass and golds in the rest of the uniform (but if you could find a black and gold/brass day sporran go for it.

Kathy Lair sells a K-Bar sgian dubh you could incorporate also.

And as always, these are just my opinions, your mileage may vary.