How to find p2p registry of blockchain participants, miners, transactions?

Question

bitcoin

Hello guys!
I'm trying to sort out the crypt and blockchain in my understanding, a couple of questions arose.
I'm using bitcoin as an example. I want to understand the essence, and not how to use the software out of the box, I got stuck a little, please tell me:

Question about P2P in crypto: to connect at least 2 people over the network, you need a server and a client, i. the client must know the ip and port of the server.
How do miners and participants in transactions find each other? So I want to send btc for example, who accepts my request? Where is the request sent after clicking submit? Should there be a single server of some sort? Like a TORRENT TRACKER. Those. directories of the transaction queue for processing and miners. What is his address? And how is it protected, is it really not ddos ​​or nirazu?
And if a miner found that magic key with zeros for a certain block of transactions, how does he find network participants to share it?

And the second question is: what if the same transaction falls into two blocks or more blocks, my block chain will ignore it? How is synchronization of billions of blocks achieved if there is no single transaction queue?
Thank you! I'm really looking forward to the answers