Ooh, exciting - I love travelling and Europe, especially. I haven't done any hitchhiking through Europe so I don't know how easy or safe it is but I do recommend taking the local buses around, as well as busing from city to city or country to country. I found that was the cheapest way to travel around, and you meet interesting people. Plus, it is a lot more affordable than taking the train, although it does take longer.
In my experience, couchsurfing is generally safe and a good way to meet local people. Also, I would check out Air BnB if you can't find a good hostel or a couchsurfing person to stay with - sometimes you can find really great deals.
I highly recommend checking out Rick Steves' stuff online (
https://www.ricksteves.com/) - he has some great packing guides and his tour books are awesome. I would go and make copies of the walking guides from the cities you will be for sure visiting from his books if your local library has any of his stuff or I think he offers some mp3 city walking tours for free on his site?
Also, I really recommend buying a travel towel. It's the best investment you can make because they dry fast, pack up teeny tiny and you can use them for a ton of things like a towel if you go swimming, picnic blanket, extra blanket if you're cold in a hostel, etc. I thought they were totally gimmick-y but then found that it was one of the most useful things I've brought with me on several trips to Europe!
Bruges is super gorgeous in Belgium, you're going to love it! Be sure to have the chocolate there, it is expensive but worth it! If you are going to the Black Forest, I would definitely go to Rothenberg (Rothenburg ob der Tauber) - it's a well preserved medieval town that has all that characteristic charming fairy-tale look to it.
Have fun!!