How many extra wallets can I buy? / What are the maximum number of Rupees I can carry?

You can only buy 3 extra wallets from Beedle, each with a capacity of 300 rupees giving you an additional capacity of 900 rupees.

The largest wallet that I was able to obtain was the Giant Wallet which you get from one of the special quests.

You get it from Batreaux after giving him 50 Gratitude Crystals.

That gives you a base capacity of 5000 rupees for a grand total of 5900 rupees when you include the extra wallets.

There is an even larger wallet, the Tycoon Wallet which gives you a base capacity of 9000 rupees bringing you to a grand total of 9900 rupees carryable max.

You get it from Batreaux after giving him 80 Gratitude Crystals.