I have created many eBay accounts over the years. The best advice I can give you is to focus more on quality and not quantity. Unless you really know what you're doing, the more accounts you make in a short period of time the better chance you could make a mistake that would link all the accounts.
I'm sure it would be perfectly fine to register 5 new Amazon accounts at one time. My suggestion would be to register 5 and organize them all on a spreadsheet of some kind. Then, work only 2-3 until you can get those up to the $1,500 and under per month (3-6 month) before you start the others, and keep in mind those others will be nice and matured for those 3-6 months when you start selling on them.