This is something that I have been delving into recently.
Initially, I would suggest that you start with EFN.
As has been mentioned, EPR is a requirement for both Germany and France.
If you google it, you will find lots of information about it.
Bear in mind that the FBA charges for EFN are a fair bit higher than standard FBA.
So it does work as a toe in the water, to test out the markets.
When using EFN, VAT is removed from the UK price, then DE/FR etc VAT is added on to the selling price. Amazon then remits this instead of you.
There is also a charge to the customer of 3.99 euros for postage that you do not receive.
If you then decide to go down the route of PanEU, I would suggest that you look at France to import any stock to rather than Germany. Lots of issues with it.
You don’t have to register for all countries to join PanEU, so you could start off with just France and Germany, which are of course the biggest markets.
This of course requires VAT registration for each country you store stock in.
Fortunately the charges for administrating this a relatively cheap if you go through Amazon.
And lastly, there is a very long running thread about Germany etc in the FBA forum (I think). Probably worth a read when you have plenty of time.