Ideal length for my trip?

How long should I stay for my first Europe trip? I’m from Sydney, Australia, and this will actually be my first time leaving the country.
Main countries are Germany, Denmark, and Sweden but I’ll probably spend most of my time in Germany and Sweden since I have relatives there and can stay for free.
I want to properly experience the countries. I want to explore cities, smaller towns, nature, hiking/mountains, nightlife, culture, lakes, trains, etc.
I was originally thinking 4 weeks, but now I’m considering 5 weeks. Since it’s my first overseas trip, I’m wondering if 5 weeks would be a much better experience and less rushed.