1 Node with 1 Relay to produce and validate all blocks.
The INV stake pool is up all the time. When not producing blocks, it is validating them.
Secured servers, with offline keys protected in a physical vault.
cardano.org has fully described what staking is, and why it is important to the overall health of the network. As will all things on the block chain: 'Don't trust, verify'. Here is their write up on how to stake.
This video by 'Crypto Capital Venture' outlines how to stake on the network...
Read up on what the heck a 'blockchain' is and how did it get to be a 2 trillion dollar banking mechanism... with no bank involved.
In crypto you are in full control of your funds, this requires getting up to speed on how to protect your hard earned $ADA.