Bitcoin Steem Similarities?

I don't know if I asked you, but does Steem allow for anybody who runs Steem on their computers, servers, etc, to be a witness, technically speaking, similar to how anybody who is mining Bitcoin is technically a miner?

Witnesses vs Miners

I know Steem has the top 20 witnesses, but is the 21st witness still a witness? Are there limits to how many witnesses there can be? Does a witness have to be voted for in order to be a witness?

Peer to Peer (P2P)

I would prefer that Steem allows people to mine Steem like people mine Bitcoin or to be Steem witnesses similar to how IPFS and Bit Torrent works. I don't know if Steem allows for this already or not but that is what I would prefer, that anybody can run Steem to help decentralize Steem, to help backup the data running on Steem as the more the computers the better.