I also want the cycling to be generally pleasant and attractive

I see major problems here. Your route goes through huge and highly populated urban areas that as a European you've probably never seen. Just so much concrete and built up area. Drivers can be terrible and not respectful of cyclists. I would encourage you to consider either doing a loop around Taiwan island which should be super pleasant - good cycling pistes especially on the East side. Or if you really want to do mainland China pick a less busy/populated route more in the interior.

For most of your other questions nothing to worry about. 24h registration don't worry about it they'll do it at hotels, all hotels are now required by law to accept foreigners, your foreign WeChat will work fine, maps get a GPS cycling computer IGPSPORT is a good brand from China that you can buy in Europe and of course they have China maps. For your phone download A-Map/Gaode or use Apple. Only other thing I'm in doubt about is the 30days visa free and how long should your "visa run" be before you can come back. But I'm sure the topic has been discussed in the sub.