Your FeedbackExpress plan is based on the number of emails that you send and the number of ASINs you want to track. You should try to work out about how many emails you're likely to send and then select a plan which covers that.
For example, if you have 3 campaigns and expect each to send 1 email for each order, this would be 3 emails per order. If you have 1,000 orders per month, you would need to have a plan which allows for 3,000 emails per month. So in this scenario, you would need the up to 5,000 email plan.
And let's say you wanted to track 500 ASINs for product reviews, you can then add the 500 ASINs tracking pack to your subscription plan.
See packages and prices here.