Transaction propagation I`ve got one really basic but still important question that is very confusing:
Does the newly created transaction needs to be propagated to ALL nodes in the network in order to be validated?
Lets suppose I have made some payment and it needs to be added to the mempool of few miners to be included in the next block. How many nodes must validate that transaction so that it will be added to the mempool?
Thanks in advance!
Does the newly created transaction needs to be propagated to ALL
  nodes in the network in order to be validated?


No. The nodes relay valid transactions to each other. In corner case you can send your transaction directly to miner node. No one will have this transaction until it included in block