I had great fun on the Talking Drupal podcast, where myself, Will, and Finn shared thoughts and experiences of the LGD distribution that we've been working on.
Drupal currently supports IE11, and will do until Drupal 10 in about a year's time. Here's my proposal for how to support IE11 in a distribution without holding back from modern CSS.
We often end up with a lot of templates when theming, but we should also remember to create "sensible defaults", so before you start theming specifically your site doesn't look broken.