You can do it for free...
you do not need to pay, but if your uploads are useful to others they will pay you.
Just check this site.
http://upload-for-earn.blogspot.com
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You can host a Minecraft Server from your computer for free (although you have the cost of internet upload). But, if your computer isn't powerful enough you can hire a server for an amount of money.
Yes it do cost money
No not unless you buy the full version of the app or something in the app.
It does cost money. but you can download it illegally
No. Demos for games do not cost money.