Goodness, what a lot in one go! I've answered what I can remember.
1. Beijing Hotels.
We stayed in the Peninsula Palace in September and thought it was really good for location and food. Would definitely recommend it.
3. How tough is immigration/customs at PEK. Time taken etc.
This used to take a while a few years ago but last year it took us about 10 minutes to get thrugh after coming off a 747. The airport has improved a lot in recent years.
5. In terms of walking, how suitable is Beijing.
The distances are usually further than you'd think. Taking a cab is OK. You will be a bit over charged but it's much cheaper than here anyway. Make sure the meter is on and take your destination on a card written in Chinese.
6. Is it a safe city for a solo traveller who does not speak Mandarin/Cantonese.
Yes, a lot better than most Asian cities! Last year I went with my husband and a few years ago I went on my own and both times I felt safe. As in the taxi question you will be overcharged a bit but the actual sums are quite small.
7. In terms of exploring the Forbidden City, Tianenmen, Temple of Heaven etc would the hotel have a sort of day tour and what would the charges be like... Or is it just better to ignore this and do everything individually.
Really you can do this with a good guidebook as the hotels will charge a lot extra. Even on my own I went to places and was fine.
8. Great Wall: How expensive will it be to hire a guide and car thru the hotel for a day trip.
We hired a car from the Peninsula to take us there. Last time I went to Badaling but this time I wanted to go to a quieter area. We got the car to take us to Jin Shan Ling, from there we walked to Simatai where it picked us up again. Fantastic walk but tiring - four hours or so. Much better than Badaling was, more atmospheric. We can't remember exactly how much it was but we both felt it was really good value as it's several hours outside Beijing and the car had rear seatbelts (useful!) which the local taxis don't.
10. What is a reasonable amount to allocate as a basic perdium in PEK for food, transport etc.
If you eat in Western hotels all the time you could be about £50 per day but if you try the good local places £20-£30 should cover it easily.
11. Should one purchase some Chinese currency before getting there, or leave till reaching PEK.
I think you have to leave it until you get there as you can't get it outside the country.
I was in Shanghai last year too so would be happy to answer any questions on that if it helps.