I just want to understand and know if in a complex FLOW, to have less CPU and RAM usage, is better or is the same things:
A) Use ONLY unique and ONE "telegram Receive node" ( and use a "function node to split the different commands received in the different line of the flow)
B) Use one "telegram Receive node" for each command I need to use and so, have 20 "telegram receive node"?
I don't think it will make a massive difference to be honest. You are only defining a single connection anyway.
Personally, I tend to keep the number to a reasonable minimum but that is based on most of my inbound processing being on the same flow tab. If I needed to split it across multiple tabs, I'd most likely use another receive node on each tab.
I would certainly not want to go overboard about having everything going through a single function node because that gets unsupportable if you aren't careful.