Question About Advanced Nmap Technique and Netcat

hello,

i got some questions:

1. if we make a 3 way handshake connection with a web server (sT), the PUBLIC IP is the one that showed up in the server logs right ? If so, can you use another person public ip as a DECOY (-D) with nmap ?
2. as for spoofing the IP while scanning with nmap, is it refer to using proxy ?
3. which is more stealthy, netcat or nmap (-sV) for version detection ?
4. i read that I2P can make your scan with nmap more stealthy, is it true ?

any information helps, thanks :)