First, you need to know that users don't pay for security
But it is worth knowing that the incentive received by the miners encourage them to keep on mining. The incentive consis of the block reward which is decreasing every after mined 210000 blocks, and gradually transaction fee is replacing it.
Nodes equally don't set the fees, basically what they do is they receive transaction when you broadcast it to the bitcoin network, they verify the transaction and relay it to other nodes (both mining node and full node) in their mempool and then mining nodes pick this your transaction and include it to get verify.
A mining node may not contain the full blockchain or pruned, just like those miners that join mining pool. What is important is the node that has the full blockchain or pruned and has routing function. Solo miners, mining pool operators and other nodes with full blockchain or pruned would be what you are referring to.
Each nodes have its own mempool. Mempool consists of unconfirmed transactions.
