1. Because RAM chips are not dense enough to be that large without using huge "sticks", and there is no need for that much RAM anyway. Also, 32-bit systems cannot use more than 4GB of RAM.
2. No, you cannot store anything on RAM, since RAM is erased when you reboot/turn off your computer.
3. Yes, see #2.
4. Yes, homemade RAMdrives are possible, but require some effort. I have no links on how to make them, they are fast but expensive.
<font color=orange>Quarter</font color=orange> <font color=blue>Pounder</font color=blue> <font color=orange>Inside</font color=orange>
Don't step in the sarcasm!