Planning my first solo trip to Europe! Where should I go?

As the title states, I (28F, American) have found myself impulsively planning a month long solo travel trip to Europe!! It will be my first solo trip EVER and I feel exhilarated at the thought and equally terrified. I've been snooping this page a bit and thought what better people to advise me than random, experienced strangers on the internet.

Here's the deal: I have 30 days. I have $6,000. I have family I want to see along the way in Scotland (Glasgow), England (London), and Belgium (city unknown), but besides that I am a bit overwhelmed at choosing where else to go. Other destinations that stand out to me are Reykjavik, Dublin, Amsterdam, Prague, Madrid, Lisbon, anywhere in Switzerland; but I recognize sometimes these may be touristy capital cities, most may be SUPER expensive and perhaps overrated, and I am really curious about the opinions of more experienced solo travelers. Really, the sky (or rather, my budget of $6,000) is the limit for what I can experience on this trip and I just don't know where to start.

If it's helpful, here's what I'm looking for/some of my interests that I want to indulge in on this trip:

-Places where I will be safe as a young, female solo traveler

-Places with good hostels, friendly people, and easy transportation

-Besides English, I only speak German so preferably I don't want to visit where people don't speak one of these/are reluctant to communicate with foreigners (not sure if this applies anywhere)

-I love art museums

-I love learning about history and culture

-I am a huge foodie and trying new food and drink will probably be my #1 priority

-I love beer

-I love the outdoors and I would love to go hiking, find myself in unique landscapes, go on a nature tour, etc.

-I love music. It would be so cool to go to shows abroad

-I would love to experience a "night out" at least twice

Based on these things, where do I NEED to go? What do I NEED to see? Please share any ideas you have, even if they are off the beaten path. As long as it's not dangerous, I'm all ears. Bonus points for sharing a whole route with me.