1. Do I need to have my national insurance number first before applying for a travel insurance? Is travel insurance very necessary in applying for the visa?
NO NO
2. Do we need to book the date of our holiday and flights first?
NO
4. How long would it take to receive the visa if granted
USUALLY ABOUT 1 WEEK
6. If I will apply for just a single entry this year, can I apply for another Schengen visa the same year?
YES