I have a major weakness for lapsang souchong. And the Twinings one, while maybe arguably not the best I ever had, is a rather canonical LS, and a comfort tea for me. Yes, it is smoky, but from somebody who hates cigarette smoke, it´s a very different type of smoke.
From experience, I do not think this is too high in caffeine.
From experience as well, and I know this is so heretical, i think I prefer the Twinings tea bags for this over the loose leaf. Perhaps I undermeasure, or the loose leaf has aged too much, or the contents of the british-market teabags are better than the continental tin caddy, but this is one of those instances I think the teabags (the black british no-string teabags) do taste more and better than the loose leaf.