did you travel with Freccia Rossa or Italo ? Those are the main high speed lines but they are more expensive which isn't the best for a group of friends

Nice list. If you want bars and clubs you should add Berlin to your list ;)

It hurts looking at that list, all that travelling and moving around so fast in such a short time, damn.

In Amsterdam stop by here to get some fries. I used to get them for lunch whenever I could, best fries in the world
https://www.tripadvisor.ca/ShowUserReviews-g188590-d1935384-r150171595-Vlaams_Friteshuis_Vleminckx-Amsterdam_North_Holland_Province.html

Dude you're rushing it. From your list I gather that you're probably not much into hiking, taking the scenic route, gorgeous landscapes and rural towns and villages (God, you find the BEST fucking bread in little french and spanish villages. They usually still have a genuine baker with a fucking wood fired oven.), so you'll probably be fine with your pace but you're cutting out the best part imo. Also since most of your vacation will be spent on planes probably, be prepared to be exhausted and tired a lot of the time.

As fas as recommendations go, you have a tight schedule so it would be good to know what you're interested in. Is it just nightlife? Or are you interested in landmarks and cultural stuff too?

Paris alone can easily be a week long trip, if you even want to get close to seeing all the worthwhile stuff and have a chance to really dive into the nightlife.
A day stop in paris is only fine if you're spending three weeks in the country and have been there before imo. You need about a day for versaille, same for the Louvre, while half a day will do for the Eiffel Tower (I'd actually recommend doing it right before dusk, you get to see the city by last daylight get to watch the sunset and the gorgeou city by night), At that point you haven't even seen the catacombs or champs elisees or any of the city really, or had delicious macarons and ice cream.

Stay away from people trying to sell you stuff on the streets. I've noticed these people in italy and france. They don't exist in germany, though.

And wtf? No Berlin? The future capital of Europe :P

Those are some quick stops in a lot of locations. Will probably be tiring, but exhilarating moving around so much.

Your first stop is Dublin. You'll be there for a Thursday and Friday. Things to see- well take a walk around the city for one, provided it's not pissing rain. It's not that big, and you can see a lot of it just walking. Go from Stephens Green to O'Connell street or vice versa) and wander through side streets that peak your interest and explore Temple bar. Go to the Guinness storehouse, see how the famous brew is made and taste a pint. If you're interested in history, the Irish Emigration Museum, Trinity College-Book of Kells, or Kilmainham Gaol will paint a good picture of our past.

Thursday will be quiet in some places, busier in others. Friday will be busy everywhere. It depends what type of scene you like, but South William Street has an eclectic mix of venues (try South William Bar or Pygmalion). Temple Bar is full of tourists, but also quite good as it has a mix of different traditonal and modern bars, also a gay club called The George. I'd recommend moving to a few different locations throughout the night to find a spot you like, as everything is pretty much within walking distance. I've always found the best nights in Dublin to be when you only have a vague plan, and let the night take you where it goes. Some of the bigger clubs are on Harcourt Street, next to Stephens Green, but they tend to be a younger crowd and a bit wild, again it really depends what you're looking for.