Ewaan at The Palace is super chilled and lovely, my husband and I go together a lot. Great food, good booze, live jazz/Spanish music, not loud but more lounge music. Love love love!
They are really awful. In the U.K. They work for you as well as the company, in Dubai they just don't seem to care or try. I'm moving out in a April, starting with the Dubai office of my company and have to recruit, god knows how I'm going to manage it!
A raincoat and umbrella would definitely be advisable! A wheelchair might be tricky, I'm not sure where you'd be able to get one, perhaps e-mail the hotel and see if they can help you.
The BigBus Tour is super easy to buy as you get on, no need to book in advance.
Some of the attractions, London eye, London dungeons, Madame Tussauds etc can be cheaper if you buy them in packages online in advance, you can also skip some queues if you book a time slot in advance.
Museums are mostly free (well, there is a suggested donation and some special exhibitions you have to pay for), there are some queues inside for some of the more fun bits (the interactive bit in the Science museum for example).
Have fun, I loved London!