Jack the Ripper

Yes! The inclusion of the capitalized 'Monstrous' in his typeline makes him a Monster (and thus Evil).

When Jack the Ripper is cast (before he even enters the realm!), his ability is put on the storyline to resolve in the future, when he enters the realm. Silenced upon entering the realm: His ability is already on the storyline, so it still resolves. (A silenced minion can still kill other minions.) He does lose stealth due to silence. Disabled upon entering the realm: His ability is already on the storyline, but when it goes to resolve, he cannot actually kill anyone, since being disabled prevents a minion from taking any actions granted by an effect. He will also lose stealth due to being disabled.

Yes, but if cast to the void, he will be banished before the rest of his cast ability can resolve. If summoned underground or underwater (or to any location with an effect that would kill him) he will die before he can complete his task as well, assuming he doesn't immediately gain the ability to survive in that location. This means he will neither Silence nor Kill his prey.

Jack will enter at the King's location and will technically change control briefly to the controller of the King of the Realm, but his ability will already be on the storyline. Jack will then silence and kill the King, and return to your control.