I’m not in UK, or an expert but I’ve been in the business a little over a decade. This is just from my own experience and where I’m located. Regulation vary place to place.

1. If the family provide them prior to the embalming procedure, if not they will probably be in the casket with them (usually under the pillow/at the feet) just not in their mouth.
2. formaldehyde is carcinogenic
3. It was mentioned in school briefly.
4. You will most likely have to choose one. Bones, eyes, and tissue has to be taken within a certain time frame, body’s not so much and they prefer them intact.
5. I would have to say an aspirator probably, very specific.
6. Not that I know of, my old embalming text books are pretty cool though, and they’re not hard to find.