Gigabytes?! It should NOT be much, unless it is a combination of 1,000s of minecraft mods. Minecraft mods take up very little space. Just be sure to have winrar or 7zip.
Definitely
Minecraft shouldn't take more than 1 or 2 gigs of free memory if you are not doing much(example, mining, idling on singleplayer) If you are on a heavy traffic Minecraft server, or if you have a lot of mods, Minecraft could use from 4 to 10 gigs of free ram. If you are asking about hard drive, it can be around one half to one gig of hard drive space.
Fix your Java, for example if you have a 32bit pc, use 32java, if you have a 64bit pc, use java 64 bit, or clean out your cache and memory, minecraft needs to have good performace and good backup space (~1 GB)
Simple delete the stuff you don't use
5 GB
Yes, you can use your local drive to store all of your work. Skydrive is an option and you get X free gb, more storage is option at a price.
One GB is a start, but it'll use all the memory you have.
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Yes, there is a free option. For now, the free account offers 10 GB. If you want more space than that, you must pay to upgrade (or use a different website).
I'm assuming you mean "How many Gigabytes does World of Warcraft use or take up?" The answer is approximately 17.5GB. That is the size of my file atleast.
Yes, unless the creator charges for it. Many just use adfly.