That is unlikely, as even a lean version of World of Warcraft would be 9-10 Gb easily. There are also a lot of patches to apply, and the next expansion, Cataclysm, will still require more content to be added.
If you want to save space, it is possible to remove the downloaded patches and store them somewhere else - just remember to keep them in case you want to quickly re-apply patches at a later date.
An 8GB USB unit
The best place to buy an 8gb USB stick online would be from Amazon. They are the largest online store, and cover most of the world in their postage, so this should not prove a problem either.
About 8000
Yes
2500-3000songs
It is possible to buy 8GB USB Flash drives in many places. Online there are a number of specialist retailers such as MyMemory. Most electronic retailers sites and sites such as Amazon will stock USB drives. On the high street you can obtain USB drives from all the major supermarkets.
When it comes to flash drives and SSD's, bigger has more space and its faster. Going from 4GB to 8GB will not be a noticeable effect. Only 2GB to 120GB will be noticable.
The cost of 8GB of RAM depends on the speed of the ram, the vintage of the computer it will go into and of course whether it is for a laptop or desktop computer.
Connect your USB drive, then click on Start then Computer. Then right-click on the USB drive, now click on Format then OK.
If by Disk Drive you mean a hard disk, then it is still possible to play World of Warcraft from a USB stick. Assuming you have a USB 2.0 port, that should be fast enough. Simply copy the entire WoW folder onto the USB stick (which has to be about 20 GB in size) and it will run. I assume however that you have a hard disk, or else you'd have no Operating System, Drivers or anything else installed. WoW does not require a CD or Floppy drive to play at all. You can transfer the entire folder by USB as explained above, or you can reinstall the entire package by going into your battle.net account, clicking World of Warcraft and downloading the game files from there.
There are several options in order to buy an 8GB USB memory stick. One example would be to check a local retail shop for consumer electronics and computer components. Another possibility would be for example online shops like "Amazon" or "Best Buy". Both have some great offers for USB memory sticks.
Yes, just copy your world of warcraft folder on to a usb drive and you can load it on any computer. I have also done this with an ipod at school. You are able to do this but you need a large enough USB Drive. To put WoW onto a USB drive it'd have to have a capacity of around 30GB+ to hold the game, all the patches, addons and stuff like that.