As another newbie (I'm about 2 weeks ahead of you John, having acquired what must have been the only Skywatcher 200P in the country until more stock arrived recently) I concur about the 8mm BST. I did quite a bit of research before getting it as my first (and so far! only) new eyepiece. I'm pretty impressed with it, both as a piece of engineering, and in use - luckily I've had a couple of nights of decent visibility to try it out 😀.
My main newbie mistakes to date have been 1) not realising that the little thumbscrew at the base of the focuser had to be loosened before the focuser would move 🙄, and 2) believing that the thumbscrew on the guidescope mount would hold a guidescope when the OTA was elevated to vertical (somehow it had come a little loose; luckily the guidescope bounced with no more damage than a scratch on the paint).
I have to say that I am one of the few that thinks the kit 10mm is quite acceptable. Seems to work well for me, I guess either my eyes are really unsophisticated, or maybe I just got a good one... But even I can see the BST 8mm is much better!
Simon