All the places you have mentioned are cities - except Belgium. Belgium is a whole country. Where in Belgium did you have in mind?
Thinking in terms of nights is easier than days. Two nights yields one full day. When you say 2 days in London do you mean 3 nights, or 2 nights?
Are your travel days in addition to these, or part of them?
Is there a reason you are backtracking out of London? More efficient would be London - Paris - Belgium - Amsterdam - Berlin, then it is all in the most efficient straight line.
London - Amsterdam - Belgium is also backtracking.
I'm also intrigued why you placed this question in the Belgium section of the Helpline? Is there a particular focus on Belgium, rather than putting the question in either Transportation or General Europe?
The reasons for the questions are so that we can best understand your plans and needs and desires, and best provide the answers that you need in return.