Your best bet is to compare all of the chips on the m'chip site. Click the checkbox on the left and then click compare (or whatever they call it). then you'll see the exact differences. Then read the datasheets and you'll learn more.

To be nice, here are a few answers...
The Enhanced UART just has more features.
Program memory; kbytes is the amount of physical space in the chip. Kwords is when you take the kbytes and divide it by the bits per program word. In reality, kbytes is irrelevant; you only need to know kwords.
The 16F88x series is NOT the same as the 16F88. In general, you can always tell if a chip is "the same" when they are in the same datasheet--if not, then they vary significantly enough to warrant a new sheet. You can read the datasheets to get the exact differences between the two series, but they are too numerous to list. The 16F88 series was sort of a ground-breaking chip, setting new standards for the PIC in power consumption and other features in a small chip--years ago. The 16F88x was introduced a few years later, and has more features/memory, etc.