Not OP but have a question if you don't mind as I just swapped to Klipper and everything isn't clear yet.

When you say "due to lack of power..." isn't klipper doing all the work meaning that board don't need to process anything and is basically in a "reader" state?

Unless you want some specific schedule, there is no need for automation, add config to yaml and it is good to go

Just use generic thermostat https://www.home-assistant.io/integrations/generic_thermostat/

Professional printing services are usually expensive, might be better to buy a second hand printer if you already plan to get one. Don't know the market in Japan but I guess they will charge you much more than 50€ and you can get a second hand printer which originally cost 400€ for maybe 150-200€.

Unlike a 1000€ printer, you will have a learning curve but you can get as good looking print as a 1000€ printer. Main difference is plug and play (yet still have to learn slicer settings and how each settings interact with each others) and printing speed.

Also, while you may choose from printing services what material to use, I ain't sure you can tell them what settings to use. As they are a printing services, you shall only tell them what those stl are used for and they should adapt according to their knowledge because they are much more than filling to take into account like walls, infill type, layer thickness, printing speed, print orientation...

Pla should be fine except maybe for the part that goes around the cylinder (depending force that is applied to it and thickness of part). In this case, petg or abs might be better

Instead of printing services, another possibility is to check the different fab lab in Tokyo, contact them and see what they offer.

I cannot see images ("these"), but if you are talking about some wheels, yes they should not be too tight neither too loose. Once tightened you should be able to turn them with your fingers without raising gantry but you should also feel friction.

I'm no expert so not easy to answer to your questions with many details. What I know is that z2m support more devices than zha, get updates more frequently, can be running separately from ha meaning that if ha goes down for any reason, you would be still able to control your ZigBee devices (I personally run it with HA), for some devices z2m expose more informations, also you can ask support for devices.

I said it is better because it is a general consensus from users but if zha works good enough for you then you can stick to it but if you encounter limitations/problems, z2m might be the solution. It is easier to start with zha but in long term, z2m offer more capabilities.

No particular tricks, maybe it's a one of the limitation of zha. As an exemple, I recently replace a bulb by a new one and old one was repurpose somewhere else in the house, the only thing I did was to rename old bulb and added the new one with old bulb name.

Actually home assistant made it happen this year https://www.home-assistant.io/blog/2022/12/20/year-of-voice/

In winter, you won't need to care much as heating will help to keep low humidity, the rest of the year, I would say you can keep pla roll out about a week before storing it but personally (living in 60-85% humidity climate), I just let it out so I'm ready to print. If I start a print after about a week, stringing will likely appear but if stays out for about a month, filament will become brittle.

Damn, if I had more electronics knowledge I would have build one. Does it actually integrate with home assistant?

Many reason to prefer ZigBee, can handle more devices than WiFi, better security as it is separated from WiFi devices, mesh system, response quicker than WiFi, low energy, built for smart home (unlike wifi), and a few other reasons I don't have in mind at the moment.