Your proposed Itinerary looks reasonably well organized. It's nice to see that you've allowed at least a couple of days in each location. Keep in mind that you'll have to allow for your two flight days. You'll often arrive in Europe the day after you depart, and the final day will be spent on the flight home.
As others have mentioned, the trip can be done in either direction. Check airfares for each option to determine which is the most favourable.
As this is your first trip to Europe, I would highly recommend reading Europe Through The Back Door, as that provides a lot of good information on things like Itinerary planning, transportation, etc. Once you've got the trip worked out, use the country or city-specific Guidebooks to plan hotels, restaurants, sightseeing, etc. Note that many of the books are also available as E-books, for those that will be travelling with an iPad, Kindle or other device. If using E-books, be sure to check the version date to make sure you're not getting last year's version. Some of the books are available in "Pocket" versions which are easy to carry around while touring. I was in Paris in July, and found the Pocket Paris to be a great reference to have on hand. You could also download some of the free audio tours for your iPod or iPad.
Regarding "staying in Hostels", were you considering private rooms or Dorm rooms? In one sense, Hostels might be a good option for at least some of the places you're visiting, as you're more likely to encounter other travellers in the same age group who will have information on the liveliest night life spots (the Hostel staff will probably also have some good suggestions).
Regarding "places to see/go", it's difficult to make suggestions as which sights to see will depend to some extent on your interests. What prompted this desire to visit Europe at this time? The Guidebooks have lots of good information about the main sights in each place you're visiting, so you can use those to plan your touring. As you're only in each city for a short time, be sure to plan efficiently so that you don't waste ANY time. One point to note is that some attractions are closed on certain days of the week (ie: the Louvre in Paris is closed on Tuesdays), so you'll have to plan around that. The Guidebooks have information on opening and closing days.
Finally, I agree with a previous suggestion that you skip the "paris day trip". Paris has more than enough sights to keep you busy for a few days.
Good luck with your planning!