1.) It is far better to book hostels in advance (via internet or phone) because you have no idea what times of year are big for travelers from different countries. A sunday night in London might seem like it won't be packed, but what about those lovely Monday bank Holidays? You might be stuck at your favourite hostel without a room.
2.) Trains can be more expensive, but they normally drop you right off in the City Centre. Ryan air is cheap, but they now charge you to use their plane bathrooms. (also, often their airports are an hour or more away from they city you want to be in!) So depending on your priorities, make a choice. When I first started backpacking, I was totally fine with schlepping my pack into tiny random airports, then on 2am buses, etc. But after a few years of that, I realized I would rather pay 15 euro, pound, whatever, to be in the city centre and just take the local city bus, tram, underground to my hostel at a decent hour.
3.) You can save money in soooo many ways! Only problem is, traveling is so addictive that I spend most of what I make on my next trip
4.) That 'creepy' 50 year old man is probably just trying to save money too! And he's not creepy, he's just doesn't speak English!
5.) You will always find a native english speaker. Aussies tend to congregate around other aussies, British people will refuse to speak the local language so you'll definitely hear them (no offense, i love my current homeland and it's people!), Americans are loud even when they don't mean it (don't worry, i'm american, but yeah, i'm loud even after living in Europe for two years!), Canadians, less loud, but you will hear them too, normally talking about how they live near Vancouver or Toronto and proudly displaying the maple leaf!, Kiwis you will know because of how they prounounce the word 'Six' (sex, hehehehe), and south Africans because they have that accent that NO ONE else has!