Thanks for the great responses folks

@Xixillia and @Mercurio - thanks for those video links, awesome to watch.

Solid advise from everyone else, I do think I need to avoid the distraction of creating another team. Focus on mastering the one group (which I do love) and bossing heroics will make me understand if I'm capable and enjoying it enough to bring on the extra challenge
I have previously tried 5 boxing in BC, but that was Mac based and quite laggy, so became a bit of a headache. The PC experience has been much smoother and much more fun this time round. Levelling in dungeons too has been good to learn tanking better, and play around with mechanics and large pulls.

Hopefully I'll hit 90 before WoD arrives, and if I do dip my toes in the 10 man waters, I'll let you know how I get on