Matching is another thing. When dressing, just about the easiest thing to clash with is plaid. With an all-tartan kilt wardrobe, you're really limited in what you can wear with it. Having some solids in the mix is a big help.
Not necessarily -- Bob Martin, in "All about your kilt", addresses this very issue, and the "American perspective" on matching patterns (tartan with tatersall, Prince of Wales Check/Glen Plaid, etc.) with the "UK" perspective. I don't have my copy wi' me here at work, but it gives some good insights and perspectives on matching patterns.

Cheers,

T.