Sebastian Köln

… europeans can't build cars that work in mud, clay and humidity.

Having used:
- an automatic sewing machine in school,
- an old electric one with "automatic" pattern (never used),
- another one that needs a new motor
- and a pure mechanical "Anker" sewing machine with zig-zag

I have to say that I prefer and recommend the last.
It has already lasted 50 years and there is no reason to assume it will stop working in the next 50 years.

And there is no risk of the machine suddenly starting and puncturing a finger while working on the needle.

At the edge of Europe here. The climate can be a bit damp and we get snow in winter. Common language is Russian.

There is not a lot of infrastructure left, so off-grid should be assumed.

If you can place the display close to the probe, wired is probably the best option. No batteries to swap.

Wifi uses a lot of power, so not an option for battery powered devices.

Bluetooth is usable, Bluetooth low energy is better.

Forget GSM based things, unless you want to read the values when not at home.

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I remember that the ZigBee protocol is designed for this.
https://www.itead.cc/sonoff-snzb-02-zigbee-temperature-and-humidity-sensor.html + https://www.itead.cc/sonoff-zbbridge.html

I don't know a lot about AAC. Wiki says it was invented in Sweden, so probably appropriate for the climate.

How about combining both? AAC on the outside and wood on the inside? (I want to avoid exposed wood here because insects will destroy it rapidly, but that is probably not an issue for you.)

What about AAC?

I have recently rediscovered it while looking for insulation materials that are mold and insect proof, not a mess to install and could be produced locally (lots of limestone here) if I can get my hand on an autoclave.

There may be reasons to not jump to conclusions that fast … strange things are going on with the election.

It looks to me that there is no way to attach user defined data (to prove which payment it is) to a transaction.
As all transactions are public, anyone can claim to have made any transaction.

The only safe way that I see would be to create a wallet per user (that wants to pay with bitcoin). Then you can tell the user to transfer X to that wallet and once enough has arrived, it counts as paid.

A bit late here…

Python is nice to get started.

I switched from C/C++ to Rust a few years ago and write almost everything in it now. (Including what would be been written in Python.)

I am not sure how long the radiator would last with fresh, oxygen rich river water flowing through it.
With a stainless steel radiator this may be not an issue, but a normal one… probably not too long.