Your problem is not of a legal nature.
iTunes lets you purchase each product only once (per account). So for 200 purchases, you need 200 accounts.
I think the smallest gift card is £10. Using the same debit card on 200 accounts will probably ring the alarm bells somewhere. It definitely should. So this thing will cost you a lot of money.
Now the bummer: You need a device for the account, and Apple limits the number of times you can switch the account on any device. You can't just switch your iPhone from account to account to account and make purchases.
Apart from that, there seems to be no legal problem on the account side of things. But there may be legal problems on the content creation side.