1. You can confirm the seats on the internet, and confirm them online 24hrs beforehand.
2. One piece of checked per person.
See here
3. Depends if your 22" fits the max 6kg weight limit with dimensions of 22 x 16 x 8 inches
4. Always flown with handluggage out of LGW. Never any problems.
5. Don't know but add me to the intrigued list