Ok, again... You guys cannot prepare for these tests. I know how you feel, I felt the same way when I was invited for my first phase selection. You can practice mental arithmetics, english (if it's not your first language) and pretty much that's it.
As for the rest I can only tell you to try to give the best you can. Have a good sleep before and, do it as your life would depend on it. (since it is, in a certain sense
)
F-ROM: "should I contact them again"
You can contact the HR if you want, but if they don't tell you anything else you can expect everything arranged for the hotel. You just go to the Mercure, tell them who you are and they'll find you on the list. People working there are quite used to the guys coming for the selections of EC.
I don't actually know how many of you will be on the tests, but I would say you can expect 8-16 ppl each group (every day).
Good luck to you guys!