Holiday help

So in April 2020 im going to be flying from Manchester to Alicante.. would it be cheaper booking flights with an airline and then booking a hotel through the actual hotel than booking it through a travel agents OR would it be cheaper booking flights and hotel through agents?

I'll be going self catering for 9/11 nights haven't decided how long for but roughly how much money would I need? Food, alcohol, nights out and activities?

Lastly.. what is the cheapest website for holidays?