glen plaid is a grey check isn't it? I would therefore choose a light blue shirt- french cuff and stylish cuff links for some added flair - and go with a navy or brown toned bow tie ( matching the brown of your shoes) because of the pattern on your suit the tie should be plain, though with a bow tie you can get away with something bold and bright.
Wear a Glenn plaid suit to an evening event because I knew that the rest of the guests were going to be in dreaded "business casual" attire. Glenn plaid suit and crispy white open-neck button-front ended up perfect. Whereas if I had worn a dark suit or a tuxedo I would have stood out like a sore thumb. I should say, however, that the suit has a very aggressive cut to it. Clean lines, roped shoulders and wide, peaked lapels. The design is far more urbane than a traditional notch 3-roll-2.
Also, I'd like to wear a pocket square.
I don't know.