Whoah, a Synth Bike, that would be neat. Though with the recent ban on using mobile phones while riding a bike, I don't think I could get away with that.
The bike cargo trailer on the other hand, that could be a great idea. I'll have to check what size would fit into my small shed, but I suppose it would be a good investment. If the length of the trailer is more than half of the keyboards length, I should be able to strap it in safely. A design like this: https://www.burley.com/product/travoy/ could fit the keyboard, but not also an amp.
Oh man, the world of bikepacking just opened up for me.
As for almost being killed by cyclists in Amsterdam, yeah, we're pretty good on a bike. (And I'll admit, sometimes a bit reckless) Amsterdam is particularly crowded though, you'll be safer elsewhere in the country.
The Fender Rumble is an interesting suggestion. I had never considered a bass amp. I don't think I'll need a DI, but the price and weight are appealing.
As for the handle on the EV speakers, that seems to me just a minor issue given that the speaker is light enough to carry in other ways.