Yeah, no, I'm half-joking about Arvo getting drugged, of course - it's obviously just a narration method, like it always is with Dawn Chorus. Like you said, Arvo already dreamed up a whole nightmare, no reason why he couldn't dream up this too - this is the route of the unreliable narrator more than anything.
But it is fun to come up with theories of what's happening, don't you think? And it kind of aligns? Klaus is an irresponsible person who does whatever childish thing he wants with the smallest amount of justification even to himself, as you can learn from his and other routes, especially Jorgen's.
Onto your points!
1) it was definitely Klaus who said he cut the tomatoes - I wrote that comment while looking at the script.
2) Such details are barely ever shown in Dawn Chorus, the text is doing the heavy lifting, and the visuals are vaguely connected to the plot at best. This is not a big project, so it can get away with this.
3) I told you, bean lottery - look it up if you've never heard of it. Klaus could put an edible in the dish and whoever gets it goes on a trip! Or maybe he put it just in Arvo's plate, not like Arvo is extremely attentive, had his key stolen and then returned without ever noticing.
Also, I think we should put this discussion on hold till you see all three Mikko endings, as I realized the Big Floof nightmare is one big metaphor for Arvo's feelings for Mikko.