Well, I've read all the posts and I still don't know what "practicing crossdresser" means, or rather, what you mean by that term. If a closet panty wearer does it regularly, could it not be said that he is "practicing"? Same goes for " "true TG lifestyle". There are many full-time TGs (and especially the subset of TSs) who would characterize part-time crossdressers as falling short of being serious about their gender expression and thus less deserving of respect -- not that I agree with that opinion, but I've heard it stated many times, and rather haughtily, I might add.
I'm not being critical, just saying your questions lack the clarity needed to attempt an answer -- and I'm not sure how useful an answer would be. I sort of agree with the sentiment that if there is indeed "a line", it is wide and gray. But if pressed for a sharp demarcation, I would say it falls between the part-time (and partially closeted) CD and the full-time, totally out TG. (In a black-and-white world, all other variations are just shades of gray.) What particular point such a distinction makes, however, escapes me.