Schengen visa information site
https://www.schengenvisainfo.com/
Flights:
skyscanner
https://www.skyscanner.net/
Stay:
hostelworld
https://www.hostelworld.com
booking
booking.com
airbnb
airbnb.co.in
Travel:
flixbus
flixbus.com
omio
omio.com
Preferred hostel chains:
Wombats
https://www.wombats-hostels.com/
Meininger
https://www.meininger-hotels.com/