I'm going through this at this moment. At first I thought I had to do all the Tanaan intro quests solo due to phasing, and this is what I did. Then I noticed I could see other people... it was too late anyway and I went solo until garrison was finished.

Then I did intro quests on second toon, but I soon realized I did not have flying in second toon (new account). So doing the power levelling start would not be feasible for this one.

In the end, both toons are splitting ways now...