Short answers, pulled from the story.
The Milky Way is the barred spiral galaxy that includes the Solar System. Its name describes its appearance from Earth as a hazy band of light in the night sky, formed from stars in other arms of the galaxy too distant to see individually with the naked eye.
The Milky Way is estimated to contain between 100 and 400 billion stars, plus at least that many planets. It may also hold ten billion white dwarfs, a billion neutron stars, and a hundred million stellar black holes.
The Milky Way has a D25 isophotal diameter estimated at 26.8 kpc, plus or minus 1.1 kpc, but is only about 1,000 light-years thick at the spiral arms. A 2020 study predicted its dark matter halo edge at around 292 kpc in radius.
The Galactic Center is marked by Sagittarius A*, an intense radio source that is a supermassive black hole with an estimated mass of 4.1 to 4.5 million times that of the Sun. Its accretion rate of about one solar mass per year is consistent with an inactive galactic nucleus.
The Sun sits near the inner rim of the Orion Arm, about 27,000 light-years from the Galactic Center. It takes the Solar System about 240 million years to complete one orbit of the galaxy, traveling at roughly 220 km/s.
Edwin Hubble settled the question in the early 1920s using the 100-inch Hooker telescope at Mount Wilson. He resolved spiral nebulae into individual stars and used Cepheid variables to measure that the Andromeda Nebula lies 275,000 parsecs away, far too distant to be part of the Milky Way.
Current measurements suggest the Andromeda Galaxy is approaching the Milky Way at 100 to 140 km/s, with a possible collision in 4.3 billion years. The chance of individual stars colliding is extremely low, and the two galaxies would merge into a single galaxy over about six billion years.