2 - I have a 12 word SEED and a strong PASSWORD (a strongPassword fanatic here). Those two are enough to keep my BitCoins if something happens to my PC?
It depends. If you're referring to physical theft, the password would most probably deter anyone from getting access to your Bitcoins. If you are talking about malware infecting your computer, then most likely not. Malware can see your password as you are typing into the wallet.
3 - Do I also HAVE TO back-up (copy the file) at "Users > Name > AppData > Roaming > Electrum > wallets > wallet" ?
No, the seed will suffice. You can back it up and you will also have your labels etc backed up.
4 - Let's assume that my computer has crashed , I lost every single file on my PC... Started from scratch. Downloaded Electrum again. I have the 12 word seed. The 12 word seed will be enough for me to get back on track or I will still need the password?
The 12 word seed will suffice. It isn't password protected.