Hi  Karl

If it is a brand new PPC account with no or very little history I would advise you to start bidding on brand terms only to build up your quality score. Use exact and phrase match only. Once your CPC has come down a bit do your generic keywords research and try to find keywords that are a) relevant to your brand and its target audience, b) have decent search volume and c) affordable d)are present on the landing page of your PPC campaign. You might have to select / create several landing pages for your PPC tailed for individual PPC ad groups each with its set of narrowly themed keywords.

Keywords' components like "luxury", high-end", "quality", "designer" etc may be relevant, but it depends on your product category and brand. You can also right away add certain keywords to negative list e.g. second-hand, cheap, ebay, gumtree, amazon etc, basically all the keywords that are opposite of luxury and premium.