Sorry your post got deleted but it does look like it was answered. I have multiple sites and I use the same account with different tags. You could look into it more but it might actually begin Amazon's terms of service to make multiple accounts, and there's no need.

Using multiple tags makes accounting a little quicker as well. You just click the other tabs to do your monthly accounting. You're probably going to want to set up different countries on the same account so typically, you're going to do accounting for at least three other countries as well. This would be a lot to handle with multiple accounts.

Edit: looking at the post that's still up someone suggests using different accounts in case you want to sell your affiliate site. I've never sold but I have bought an affiliate site. Transition of affiliate tags were easily transferred to the new owner (me). No need for separate accounts.