Black seems to be the most versatile color, it works with everything. I ordered my black belt and my black sporran from the same supplier (Scottish Tartans Museum), they match very well. I am sure they were made by different manufacturers. Black is easier to match than brown.

You can always purchase the brown items later if you feel you want them. Get the solid color flashes to pick up one of the brighter colors in the kilt. I agree oatmeal hose is a good starting point and would work quite well with the kilt. I also like the matching flashes, you get probably get a pair with your kilt, they may cost a few extra bucks but are worth it.

That tartan is going to make a good looking kilt.