And if you still haven't have a merchant account, I will recommend you to simply stick with Pay Pal or 2Check Out at the initial stage for cost savings and less hassle. Of course, they can only access a public folder in your account (they won't be able to touch your private files).
That's why I would highly recommend you to pick at least the Baby plan because you are allowed to host unlimited websites under the same account. Are you going to take credit card payments by yourself?
Trust me, as long as you stay long enough, you will always have more domains, especially when you can own a new domain for less than a year nowadays. If the answer is NO, you don't need the Business plan at all.
I will try to explain the differences to you so you can make a wise decision on which plan to choose. Hatchling is the traditional 1 domain per account type of hosting. With domain names being so cheap today, you will have a very high chance of owning more than 1 domain.
That's why 1 domain per account is really very limited!