I regularly daven in a Minyan with exactly 10 people, and I had a few questions:
1. Is there a need for six people to be holding with the minyan at the time of Borchu?
No. See here:
2. To start Chazoras Hashatz, you need to wait for 9 people. Many times we have six people davening with the Minyan and a few that are behind. Do we have to wait for ALL of them to be done Shmone Esreh, – No. or is it enough that they aren’t davening Shmone Esreh, but they are still in the middle of Pesukei D’zimrah – Ok. or Birchos Krias Shema? – Not OK.
3. Even if there are nine people able to answer, but one is negligent and doesn’t answer a specific Brocha, is my Brocha a Brocha Lvatala?
It’s almost a Brocha Lvatala.
4. Do I need to wait for 9 people, or 6 people or none of the above to say Kaddish Tiskabel after Maariv?
5 people. Six with the Chazan. See here:
5. If I started davening Maariv Shmoneh Esreh, or similarly Chazoras Hashatz by Shachris and Mincha with 6 people davening, and some left in middle, I know that the Halocho is to continue Shmone Esreh/Kaddish even with no Minyan… Is there a difference if the person/people that left are from the six that davened or not?