Gentleman Coin Help

So the best way to actually get the chair is to hunt for coins at the boss room killing the batch of zombies? at X2 is prefered and with a familiar a must?

Depends on how much of a hurry you're in.
Event lasts 4 weeks, and you get about 20 coins from the daily quests (not counting Cassandra's "hold this for half an hour" repeatable one), so you could get the chair just by doing those quests for about 20 days.

But if you're in a hurry, yeah, 2x with Big Spider in the event map. The Zombie map is not instanced so prepare for crowding. I'm not sure about the boss map itself (you can enter it repeatedly).