Unless you will be staying in hotels that could take care of this for you, I'm concerned that you could use a lot of your valuable vacation time trying to find a post office and then standing in line waiting to mail your items.+1
I strongly recommend that you take some time to see the sights of Europe without your view being constrained by a viewfinder.+1
Is this your first trip to Europe? First trip overseas? If so, I'd say don't do a 50-day trip, do a 14-day trip this year, and another one next year, etc. It would be a shame to get 10-days into your trip and find that you don't really like being away from home that long, or that you misjudged your interests or stamina, etc. Traveling well is a learned skill-set.