Europe Summer Trip

Hi, I'm planning on spending 1/2 months - 2 months around Europe (London, Paris, Barcelona, Italy, Vienna) next summer. As I've been reading some posts on here, I'm still left with a lot of questions.

For reference, I'm 21F and will be travelling solo, I'll probably bring a luggage and will get some souvenirs from the places I'm travelling to; however I'll be packing very light. I understand that hostels are cheap and I am open to that, I'm just not familiar with how it works + how to book it. Basically, I'll just list my questions below, and if you have any advice please please let me knooow!

*My budget will be ~$7500CAD (i know it'll be a stretch, but if i'm spending a week or two in london, food & accomodation will be excluded from the budget as i'll be staying with family)

*I'll be flying in from Vancouver to London

*Most likely will not spend a lot in London as well, I just want to spend time with my family and look around new scenery, so most of my budget will just go towards the other cities

1.) Should I just book a roundtrip flight and figure out my accommodation (hotels/hostel) a few days before landing to the next city? e.g. booking a hotel 2-3 days before flying into Paris/Italy/Vienna/Barcelona

2.) How much are flights from London to Paris? Paris to Barcelona? Italy to Vienna? Basically what is the range for flights within Europe for these cities?

3.) Would you recommend I buy a package (hotel + flight) through Expedia instead? especially since i'll be staying a week/week and a half each for Paris, Barcelona, Italy, and Vienna. Or is it cheaper to buy the flight and hotel/hostel separately?

4.) Eurotrail pass? Do i need it? Is it easy to navigate + safe for solo woman traveller?

5.) If you have any experience on travelling Europe for cheap PLEASE SHAREEE! I am no stranger to skipping a few meals, staying in a dorm, or just simply walking around for the fun of it. I don't spend lavishly and I have visited Barcelona and loved just looking at their architecture alone, so no need to buy a lot of entrance passes for things :P

6.) How much would transportation be within these cities?

7.) If you spent most of your Europe trip in hotels, please share the costs + how it was!

8.) If you spent most of your Europe trip in hostels, please share the costs + how it was!

Just dump all the information you think I'll need since I clearly need a lot of advice. Thank you so so much in advance!