Not necessarily. A server has to be hosted somewhere, some people who run very small private servers can host it on their own machine. It can be a strain to the system and its bandwidth, you might not even be able to play on the same server yourself. The server is also dependent on your computer being on - if you switch the computer off, the server will be down.
But, if you're planning to have a lot of people connecting, then ideally you want to pay for a hosting plan, the server will be run on the hosting company's dedicated system, meaning more people can connect, and it stays up constantly.
It does cost money. but you can download it illegally
No. Demos for games do not cost money.
No, there are no additional fees.
Minecraft forge is a free program.
No, it does not cost anything.
No they don't.
no
No
Well, you need the game 'minecraft' which does cost money. Pixelmon is just a mod for the game 'Minecraft'.
Custom maps in minecraft can usually be downloaded for free.
$26.95
They cost memory. No money though.