Hello Mohamed,
1. You can't jump from a 640 kernel to a 7.x kernel like that. You will have to restore your previous kernel for your system to be useable again.
2. When you need to implement SSFS during the SUM phase "Extraction", you will have to run the required commands from the SUM/abap/exe directory as <sid>adm.
3. Yes 470 (ECC5) can be directly upgraded to ERP6-EHP7.
Please keep in mind that if your system is Non UNICODE (NUC) then will have to perform a CU&UC.
Hope the above clears things up for you slightly.
Kindest Regards,
Amerjit