I would arrive about 40 minutes before your ticket time -- you do periphery security which is pretty quick bag check then get in line with those with your time slot -- and with luck you actually get on the elevator, through security etc a few minutes before 11 so you are on the tower. FWIW. the sparkle is not very interesting ON the tower as it is from a bit of a distance. Perhaps see the 10 PM sparkle (if any) and then walk from Trocadero to the tower for your late time slot.
I would not hesitate to take the metro back to Vaneau after your visit. We go from one side of Paris to the other late at night all the time. e.g. this spring we went from the Philharmonie in Villette to the 13th late at night. The metro is fully of other travelers till it closes; it is just not dangerous or scary. Paris is not a town where violent street crime is common. You can get a cab if you like, but we would just take the train ourselves. I would also not hesitate to walk if you wanted to do that.