Travelling to Hong Kong, Japan and (or) South Korea?

Hello Community

Friends and I plan to go on a trip (from Germany) to Asia for 3-5 weeks in September depending on budget. For example if we have a budget of 4000 € for each person what should we do? The desired countries would be Hong Kong, Japan and (or) South Korea.

Someone said it is enough to stay a week in Hong Kong to see everything (which I personally don`t believe) and also 5 weeks for 3 countries isn`t long enough to actually explore it!

Could you please give us any advice regarding accommodations, food, activities and attractions in the mentioned countries? What would you do or recommend?

Please tell us your travelling experiences if you want.

Thank you very much for your help

Verena