Proper decomposition and enough time renders the material safe for application to food crops (typically 1-2 years and applied to Perennial crops as "side dressing").

That said, you must separate humanure from safer waste which may be applied as crop dressing in as little as 18 days using hot composting methods.

For more details checkout my YouTube channel:

https://youtube.com/c/RussellBallestrini

An easy compost toilet is a bucket to poo into and woodchips or sawdust which is high carbon and soaks up smells and liquids, is layered after each use, emptied into a dedicated pile oftened tarped to control moisture.

It's been a while since I've read the Humanure Handbook and I've not practiced many of the techniques in it but it does cover this topic in great detail: https://humanurehandbook.com/

I believe it is possible you just have to be really careful with how it's treated, especially around vegetables etc.

There's also a natural blackwater treatment system, briefly mentioned in this really great video from one of my favourite Permaculture teachers (EDIT: it's at 46:45), which also happens to be a great introduction to Permaculture if you're interested: https://vimeo.com/95060300

That's why all sorts of taboos exist in societies where it was common. Ask an older Chinese guy what is worse, eating fresh lettuce or smoking? Sure, smoking might kill, but raw vegetables will kill you quicker.

If properly handled/processed, it's ok. One consideration is what people are consuming to create it. For example, some medications are found in excrement. I don't know which, if any, can be taken up by plants. So this along with any other chemicals people flush would make me leary of using sewage from a sewer plant, but residential level systems have a lot more control over those inputs.

Yes. The human digestive system adds bacteria you don't want in your fertilizer.

Yes.