Not a fan of the sweet stuff, but you nailed it with the yakisoba and takoyaki. Them and beer are where it’s at.

I haven’t done this particular ride but I have done a ton of riding in both Kansai and Kanto though I haven’t ever ridden a foldable; I ride a cyclocross bike and put paniers on for longer trips. Not sure about Shikoku, but in general riding is a great way to get around Japan. Drivers are generally pretty courteous, even though the roads can be pretty narrow. Also tunnels… avoid them if you can, but often you can’t. Make sure your bike is well lit and that you’re wearing reflective gear.

The one thing you want to be careful about is the weather. If you already live here, then you know, but in case you don’t, it’s currently 32-38C every day, and will remain so for the summer. I did a longer (1000km) trip in August one year, and it was pretty miserable, plus you can end up waylaid for a couple days by a typhoon depending on timing.

I can’t imagine that visiting a bunch of temples along that route would be at all offensive to practicing buddhists - people visit temples all the time and as long as you’re not being disruptive, I can’t imagine any problems. I’ve always felt more than welcome at temples. Sounds like a really nice way to see Shikoku!

One thing about a foldable is I imagine it might be easier to pack to bring on trains, assuming at least some parts of your trip will be on the train. Otherwise, buy a bike bag and get ready to disassemble and reassemble your bike for any parts of your travel that involve a train.

If you haven’t looked at it yet japancycling.org is a good resource for cyclists. I remember reading it before I moved here 20 years ago, and it had a lot of good info - not just routes, but things that might not be apparent if you haven’t cycled here before (e.g. bike bags).

Honestly they should post this somewhere more conspicuous than a hotel in northern Japan if they want humanity to get the message, maybe at the Shibuya scramble or Times Square.

For early beginners, I’ve heard good things about Nihongo con Teppei and Japanese with Noriko.

For N3-ish to early N2 level, あかね的日本語教室 has a lot of quite short episodes that are easy listening and that review any potentially new vocab at the end.

For N2 and up, I’d recommend listening to regular podcasts in your area of interest, or selecting audiobooks from Audible then giving a first pass listen through to get the general gist, then re-listen but look up any words you don’t know and ideally add them to a review list somewhere, then give a third pass through by which time you probably won’t need to look much up. Repeat until you feel like you understood 100% or get sick of the episode/book. If you’re into computer science, I’ve found ゆるコンピュータ科学ラジオ easy-ish to follow. For general science topics, though leaning a bit towards biochemistry, biology, and chemistry, I’ve found サイエントーク relatively easy to follow and a good source of new vocab.

In terms of audiobooks, I can recommend the first audiobook I listened to, which was 神の子どもたちはみな踊る by Haruki Murakami. The stories are all relatively short and written in simple language.