Sounds like a good idea.

My only thought, is that you may be better off just making a business card of brochure to pass out to people. The booth will be a big personal expense (time and money) with little to no payback for you. Now if you were representing a specific company(ies) that were either giving you a discount on product or a freebie (does that exist?) than I could see the benefit. It is a great idea and it shows that you have a big heart and a desire to promote kilt wearing to more people, which is very admirable.

Promoting a specific company may also be better suited for a Celtic event, as promoting kilts to a group that (most) already know about kilts is like preaching to the choir. Promoting an alternative to a traditional wool kilt that can be worn day-day may see better results.

Just my 2 cents. I still think it is an admirable idea and one that I am sure you would have fun with