Were the Gospel accounts based on the testimony of eyewitnesses who were still alive when the Gospels were written?

The way the Gospel accounts use the right names for people shows that they were about real people, based on reliable information.

The way the Gospel accounts use correct place names shows that they were based on reliable information from first hand testimony.

Can we be confident that we have the original text of the Gospels? How does it compare to other ancient documents?