I would be interested to hear what your issues are around Advancement reporting from TT to SB+. First please check out this vidoe that Dave created when this system was going live. It is still correct from the TT side, a couple things have been added to the TT side but the process is still basically the same. If you still have any questions please post and I can help walk though the process. I have both a Pack and Troop that have been using this process successfully for several years now, since it was updated from the old advancement system.
https://community.trooptrack.com/t/internet-advancement-2-0-integration-preview/
The decison on when to add someone to TT will vary greatly from unit to unit. Balancing time to add vs longevity of user. If you have a good system that is working for you that is great.
I agree about the Movo system and BSA really pushing for registration right away, we also encourage visiting several meetings before signing up. I was in there today and there is a check box for Unit allows participation before registation or something like that, I checked it for my unit, not sure yet what that does yet.