First Interrail Trip - is this itinerary realistic?

Welcome.

It sounds like a great trip but, to be honest, a little crowded. Two nights is the minimum I would recommend in one place; three or four is better. It gives you time to get to know a place, and potentially take day trips to somewhere else. If you can cut one of your destinations out, you won’t regret it.

Reservations will be compulsory on the Eurostar between Paris and Amsterdam, and they’re pretty expensive (€32). You can avoid them by taking a bunch of slower trains (7-8h vs 3.5 on the Eurostar), but I don’t think that's worth it on an already packed itinerary.

They’ll also be compulsory on most of your route as far as Prague, but pretty cheap (a few € each). Thereafter, you can do the rest without reservations.

You can see all the reservation requirements and costs here. 

https://www.seat61.com/interrail-and-eurail-reservations.htm

If you were happy to skip Paris and fly to Amsterdam, you’d save yourself money on reservations and give a bit more breathing space for your itinerary.

Paris is a great destination for young people, in France the state operated museum offer free entrance for people under 26 from the EU. And many of those museums are located in Paris. (Some of them require free advance reservation) (Some Highlights: Louvre, Versailles, Arc de Triomphe, Museum de Arts et metiers… )

Do you plan on doing cooking or eating out? If you dont plan on cooking, youth hostels could be a decent option but with 4 people they are not necessary the cheapest option. (I personally stayed in one in Paris, Vienna and in Berlin)

I think 2 full days is fine for a first visit, since you can come back to places you liked on another trip. Also Paris for example is a city you often emd up in if you travel through france. Same with Vienna (i often end up there because the youth hostel is affordable and a lot of train connection go there.

Prag has a big airplane Museum with free entrance. (The military Museum close to the main train station can also be visited free of charge)

Thank you so much for your advice, I really appreciate it!

Our idea is exactly that, to see a bit of each city since we haven’t been to any of them before. If we end up loving one in particular, we’ll definitely come back for a longer trip focused just on that city.

For accommodation, I’ve mostly been looking at places in the city center. I know it’s more expensive, but since we’re staying only a short time in each place, I think it’s better to have everything close and save time.

Right now I’m mainly checking based on price, so whether we cook or eat out will depend on what ends up being cheaper. If some hostels are more affordable, we’ll probably just eat out instead.

Do you recommend any specific hostel websites, or are Booking and Airbnb good enough?

With such a short time, you want to stay near the (or a) station, or in a direct line between there and the city centre. 

I use Airbnb, Hotels and Booking. The map search is your friend, once you’ve filtered by price and any other criteria you want.

Bear in mind that you’re looking at 4-6 hours train travel every other day. With hotel check in/ check out, luggage storage, getting to & from the station, and allowing time for delays, that is taking up most of a day, so you’re only really getting one day per city. Wise use of early departure or late arrival may help mitigate this. 

The sleeper between Amsterdam-Berlin or Wroclaw-Prague (pick the sleeper up in Kedzierzyn Kozle) might help too.

Using hostels is also a good thing to keep costs down. In a lot of them you can make your own food, also helping to cut the cost.

I usually don’t book via Booking. I use it to find hotels or hostels and afterwords I book directly at their website. That always saves a couple of Euros that you can spend elsewhere.

I agree to skip Paris.

If you try to avoid the travelling in the weekends (Fri, Sat, Sun) in July and August, you’ll probably have a better experience on trains, as those weekends are probably on of the busiest travel weekends in Europe in the year.