Re: Tricky question about main quest 'Journey to Meridian' -spoiler-

1) I don't know about the outcome as I always have saved all arcs. They show at the end, but I don't know how much influence their presence has.

2) It is the last mission. But it is seperated in parts like before...So the meeting on the Nexus is not the final mission. You still have time to save the Turian arc!
    I completed several missions after talking to the leaders before I actually traveled to Meridian and triggered the final mission part.

3) I don't know if they are stuck there... I don't think so.