Memory Part 2. (Memory Storage)

This is what I've compiled so far:

Bit = 0 or 1

Bit = 1
1 Byte = 8 Bits
1 KiloByte = 1024 Bytes
1 MegaByte = 1024 KiloBytes
1 GigaByte = 1024 MegaBytes

Integer = 4 Bytes
Small Integer = 2 Bytes

I'm working with 1KB of memory, hehe. I would show the diagrams but I don't know how to display images. Just a few questions.

How many bytes is a string variable?
What does a byte address look like?
What happens if I want more variables than there is space in the computers memory?
Why 1024, and not 1000?

Thanks all in advance. :)