It is free at pretty much all the places you stay. On check in your tour leader will tell you how it works and what the password is. Most places you stay it is different. some have no passwords, some have limited usage (florence i think),some you have to go close to the modem (plitvic lakes) and some have none at all (avignon). But for the most part the wifi is good. Or though it can slow down when a bus load of 40 people all try to get on at once. You will find that you will get in a habit that every time you stop on the bus you instantly switch wifi on and try and find a connection before everyone else does and it slows down. haha its pretty funny. Sometimes at cafes/restaurants you have to ask for the wifi password but if you are buying something then they will give it to you.
I didnt pay for wifi once when i was in europe. However sometimes you can pay for it if you want. like on the bus (rip off) and on the ferry's (which were a reasonable price like 3 euro for two hours) but i didnt have the need to get on.
Yeah I paid cash for everything. I would go to an atm and withdraw a large sum of euro/pound (100-200) and then put most of it in a safe place and some in my wallet. Depending on your card company you can get charged a lot for every atm and eftpos transaction you do... like 5 -15 dollars a pop. I opened a Citibank account that gave me no charges overseas but you should look at what bank/card you are going to use and check the fees.
For the smaller countries where you are only there for one day and where their currency is worthless (so you cant exchange it in another country.. eg bulgaria) i would just take maybe 10-20 dollars out and use that for the day.
Just using your card for most transaction will maybe work in the bigger cities and countries. Most places dont have card access available. Smaller businesses/ cafes/ restaurants/little shops/ souvenir places etc wont have card services available.
Im not a cash person at all either but I would recommend using it when you are in europe, its just easier and safer. I would have in my wallet probably 50-70 euro of smaller currency notes with a 50 euro note hidden away and one of my cards for emergency. With the rest of my cash and cards with my passport in my bag at the hotel.Also coins are very handy in europe. Most places you have to pay for the toilets (20,50 cents or more) and coins are the only thing you can use. Also tipping and splitting bills can be hard when you want to use card.
Anyway to answer your question, Yes it will work in some places in Europe, but you will probably find that you will be using cash for most things.
Accommodation: Some places were great, others were pretty average. You dont spend much of your time in your accommodation but most places you stay have everything you need. Some places might be not what you are normally use to but you have to remember that topdeck chose them for a reason (ie. avignon, close to the city centre, but pretty terrible accom). After a while all we really cared about with where we were staying was that there were plenty of power points to charge everything (tip. bring a power board), that there was good wifi, and good aircon. Just enter with low expectations and then be surprised at how good some places actually are.
Breakfast can be pretty crap at some places, mykonos springs to mind, but most places will have the basic bread, youghut, and 2 types of cereal. Most of the included dinners are good.
Laundry: Washing machines are sparse and hard to find at times. there will be a list on the bus with places that will have them and your tour leader will tell you about places that are good to do washing and ones that arent. Some places have no facilities and others only have a couple of machines. When I was in barcelona i decided to do some washing, and it basically took all my afternoon, waiting for a machine, washing, then drying. It can take a while. Other places you can take it to a laundromat but the tour leader will let you know where and when to do this. It can be a good idea to split it with a friend as well to save money and time. But you may, at times, go for a week or two without having a chance to do washing.