1) You will have to check for each country. I think you can fly a German registered aeroplane into The Netherlands on a German validation of your US licence (as that is still EASA territory) but I cannot be sure. The validation applies to aeroplanes registered in the country in which your validation was obtained. Best thing to do is check with the place you rent from as insurance may also be an issue.
2) That is an additional question, it is not automatically available. This may vary depending on which country you will be doing your validation in, so figure out where you want to fly first. Then we can check the regulations for that country. Note that stuff like this is still mostly covered under national legislation, not under EASA rules (if I'm not mistaken. I'm sure someone will correct me if needed).