Yes, you can order more than one set. Just add $18 for each additional set, plus $2 for each set for US backers shipping, $3 for Canada backers shipping, and $4 for International backers shipping.
An example would be: US backer wants three sets: $18 + $18 + $18 + $2 + $2 = $58
Don't see the answer to your question? Ask the project creator directly.