Most online quotes require that you're a bog standard citizen who's lived here for 3 years with no claims and no convictions. Basically, you'll have to phone them up to get a quote.
Likely depends on whether your current license allows you to drive a bike, since they'll probably exchange for an equivalent one. Have a look here for more info:
Well, depends what you mean exactly. There are vehicle categories from A to E that define what type of vehicle you're allowed to drive on your license(most people just have B, which is normal cars). Car registration numbers have a letter at the beginning (which is referred to as "H-reg", etc) which defines the age of the car. Basically, A-reg is 1983-4, B-reg 1984-5, etc. In 2001, they ran out of letters and so switched to the new style AB01CDE plates.
The yearly car tax rate depends on emissions, and is between 65 and 160 pounds per year depending on how efficient your car is. For post-2000 cars, it's based on actual engine emissions tests; for pre-2000 cars, it's just based on engine size.
Yes, the MOT is annual for cars over 3 years old. If you intend on keeping the car longer than a few months, it's probably worth spending a bit more and getting one in good condition that won't fail the test and require a fortune in repairs every year.