If it's a once in a lifetime trip, pick one or two top priorities, design the trip around those, and you'll find ways to get what you are looking for. Minimize the attempt to achieve too many priorities at once, so you can enjoy what you do end up doing.
That said, once the basics are covered, you can add the other things where cheap and convenient. FWIW, half the joy of travel is seeing regular things in new places, such as "What is Aldi's like in Germany compared to USA?"
Last thought: With all due respect to those who say not to overschedule, there is an exception if you like the feeling of movement, and seeing many things in brief bursts. In other words, if you the train trips from place to place are a thrilling adventure, you can maximize them instead of minimize them. Trains in Europe are something special from a US perspective, at least for some of us - so if that's part of what you want your trip to be, research multi-use train passes!
Anyway, enjoy.