1) I was surprised, but it seems right, as long as you have a SimModule on your commlink. Only activesofts seem to require skillwires.
2) Yes on all accounts.
3) If you run more skillsofts than you have System rating, your response drops, which may cause a drop for System, depending on how you read "base response". So you could effectively shut down your commlink in a downspiral depending on interpretation.
4) System rating
You're welcome.