Re: Preparation for multi-destination trip?
hello there mate.. since I've been traveling a lot around the World I think I can help you..
First, when you travel in multi-destinations always prepare a plan in advance, especially if you have to take more than one plane/train/bus rather than going with a car (rented or not) .. you don't want to lose a plain or a train, do you? So make a piece of paper or an electronic document where you register the plan for your trip (you can as well include the details of the various hotels and/or places to visit, like precise addresses, phone numbers etc), the more details you have the better it will be. As obvious as it is, let me stress a point: when you are on multi-destinations if you lose one plain or train or whatever, all your plan will be messed up!, so better being prepared..
For the same reason it's always good to have 2 copies of each booking/boarding card/ticket you need (even if you have the electronic format, always have at the least one printed copy, your phone/tablet can always fail/break/be stolen). Put one copy of those documents in your personal small luggage, the other copy in the bigger luggage (the one you use for the clothes).
If you are moving around a lot with luggage and all that, you might want to consider to rent a car, at the least for all those trips which are less than 3 hours long; if you are coming in Europe, with the exception of the trafficked areas of big cities, it's normally an easy going to drive a car here.
as per your questions
- sleeping: guess airbnb would be bad for that? Are those 1-3 star hotels or hostels in eastern and southern Europe usually clean (free from bed bugs)?
any place that it's worth at the least 55-60€ per night (only the room) should be cleaned and offer you all the basic services.. price can vary upward up to 100%, but not much downward (best case scenario you can get a decent hotel for 45 €, very rare though), depending on where you are, but in general with an expense of 60 to 100 € per night you can get a good hotel everywhere in Europe (sometimes with breakfast included). I strongly suggest you to not to go to hostels, B&Bs etc.. the quality is never granted there. You can trust sites like Booking or Trivago for reliable reviews of hotels.
- luggage: better with something like 50L backpack and a small daypack?
yes, but remember that many air companies in EU area apply an extra charge for large baggage and that you need to book it in advance together with the ticket (if you take the extra luggage charge at the airport they will ask you a lot more money).
- laundry: where do I dry the washed clothes or pack wet ones? or maybe minimum 2 days on each site?
most hotels (usually from 3 stars and up) offer a daily laundry service; almost every hotel has a hairdryer in the toilet, that you can use to dry small clothes (underwear) that you washed yourself.
- disposable towels, underwear, etc?
IMO, no... most of them are crap
let me know if you have any other question