Here are all the plaques links and the answers with the questions.

1. 

Q: What does "Edo" mean?
A: (E - inlet, bay et To (do) - door), hence "door to the bay"

Clue: If you're lucky enough to catch the cat, you'll catch the key.

Shinju No Touhouya (shop in Yoshiwara)/Maneki Neko item: http://www.ancientworlds.net/aw/Article/841426

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2. 

Q: Who ordered the construction of Edo Castle?
A: Uesugi Mochitomo

Clue: This key can be found in the mist of time.

Edo History board: http://www.ancientworlds.net/aw/Board/823812

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3. 

Q: What disaster took place around the middle of the 17th century which not only destroyed a great area in Edo, but also had consequences on the new plans made?
A: Meireki Fire (1657)

Clue: Peace and meditation are the answers.

Senso-ji Temple: http://www.ancientworlds.net/aw/Post/837894

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4. 

Q: According to legends, what artefact is at the origins of the oldest temple of Edo?
A: A golden statue (of Kannon).

Clue: Seek the Devil and it's bags.

The Devil Wears a Kimono: Edo Fall Shopping Spree board in Yushima - http://www.ancientworlds.net/aw/Board/832506

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5. 

Q: What's the generic name used to refer to the beautiful women (or male actors performing a female character) represented in japanese arts, like woodblock prints?
A: Bijin

Clue: The chinese beast is holding one of the keys.

Bop Nian post - http://www.ancientworlds.net/aw/Post/498363

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