Fallen at the first

It seems my reply was a bit late, but:

why is there no wired option for the Pixl ?

It's a frustrating combination of power usage, cost, and not enough pins on the microcontroller. However if you have a USB-TTL dongle handy it's just 4 wires away

copy and paste - and invisible whitespace characters

The IDE itself should strip those out when you paste into it (especially on the right-hand side). The other issues you're having are I think a symptom of what's described above.

The 'Level 0' setInterval() thing

That shouldn't be an issue at all - it's actually the code that comes before it...

I'm just surprised and frustrated the upload mechanism is so fundamentally flawed.

If you turn on Save on send in settings I think you'll find it'll do what you expect, but there are some trade-offs.

It's just a bit unfortunate really as the vast majority of things you'd upload would work just fine - it's just the DS18B20/OneWire stuff pauses for some time when it is called.