I would recommend ensuring that the kilt is donned neatly, and not in the typical "toga/sash" manner done by most SCA folks. Many old images show the kilt being pinned over the left shoulder, with the rest neatly tucked away, the resulting look not unlike an over-sized fly plaid tucked into the waistband. It could be done up in "cloak" configuration when outdoors in foul weather, but I'd recommend having a brooch on your person to pin it over the shoulder when you go indoors.

I think that the belted plaid would look nice with a tweed day jacket, and a plain, leather sporran. I'd avoid having more than one piece of anachronistic clothing on your person... so if wearing the belted plaid, there's the one item.