Nice looking outfit. The only suggestions I have (and they are only suggestions) are these. If you are going to wear the vest and the tie, button the vest. And then, since the vest is buttoned, you really don't need the belt at all (you couldn't see it anyway).

I think an open vest looks good with a less formal outfit (no tie). Oddly enough, I do think that a belt looks fine when worn with an open vest.

The only other suggestion is that I think a brown leather sporran would look stunning -- it would tone well with the vest, the shirt, and the tartan.

Great looking tattersal shirt, by the way!