oh, and to answer your number 2), get more details here:

Bit - Wikipedia, the free encyclopedia
Integer (computer science) - Wikipedia, the free encyclopedia

basically, the bit size determines how long a "word" is to the CPU. 16bit word is 2 bytes, 32bit word is 4 bytes, 64bit word is 8 bytes, and so on.

from the point of view of a 32bit processor, a doubleword is 64 bits.

the bigger a native word, the more complex a CPUs calculations can be because it can address bigger numbers with fewer operations.