It
can be confusing operating in the EU. Whatever jurisdiction you're operating in, when it's not your own, it feels confusing! In my experience the EU is at the better end of the scale - but you have to bear in mind that it's separate states with ajoining regulations for the "market".
If you think you'll scale the business then it's best to start with a single company registered in a EU country of your choice. Generally, easiest to pick the one you will find easier to deal with, or you think you'll have the most sales in.
The local tax regulations will specify when you have to pay taxes in other EU jurisdictions. There are limited exceptions when you're just getting started. This only means registering for taxes - it's similar to the idea of US company registering to pay local state taxes.
Employing people is different and will require registering for employment taxes in each country.
Any competent business accountancy firm should be able to provide assistance: generally best to work with one which has relationships or offices in the other EU countries you're interested in operating in. If you can't afford that then your local government business department will be more than happy to help (as you are generating tax!): in the UK that's the Department for Business Innovation & Skills [1].
[1] https://www.gov.uk/government/organisations/department-for-b...