As always, I recommend Roger Pearse's excellent pages on Mithras and Christianity and myths about Mithras and Jesus.

In short, as /u/ctesibius already notes, so much is unknown. The Mithras cult appears in the Roman context between the 1st and 4th century, so overlapping with early Christianity. It has some similarities, but not more than one would expect for any religious cultus in Late Antiquity.

The most direct similarity is over the communion meal, and this is because Justin Martyr makes the connection and accuses the Mithras cult of deliberately imitating Christians.

Not known. We know very little about the mystery cult of Mithras. We don't even whether it was the same god as the Zoroastrian "angel" Mithra - the Romans thought so, but may have been confused by the similar name.

We know that Mithras was depicted as emerging from a rock (usually said to be "born" from it). He wears a characteristic hat. He slaughters a bull, and certain specific animals are present. He shares a meal with the sun (apparently the god Sol). We know that his followers met in underground or semi-buried rooms for a sacred meal. The rooms had a statue of a naked man with a lion-like head.

Of these, only the meal has any resemblance to Christianity, but other religions and cults share the idea of a ceremonial meal.

Related question: if they are true, why do these similarities exist?