Any "enters" abilities of the copied creature will trigger when the token enters. Any "as [this creature] enters" or "[this creature] enters with" abilities of the copied creature will also work.

In the case where the target creature is copying something else when Echoing Assault's second ability resolves, then the token enters as whatever that creature copied, except it's a 1/1.

If you attack multiple players in the same declare attackers step, Echoing Assault's last ability triggers once for each player you attacked.

The token copies exactly what was printed on the original creature and nothing else, except it's a 1/1 (unless that creature is copying something else; see below). It doesn't copy whether that creature is tapped or untapped, whether it has any counters on it or Auras and Equipment attached to it, or any non-copy effects that have changed its types, color, or so on.

Although the token enters attacking, it was never declared as an attacking creature. Abilities that trigger whenever a creature attacks won't trigger when that creature enters attacking.