Hi Sumaira
On the first point I find that the SLA calculation is performed on the setting of the Priority value...so if you're setting the Subject next and the SLA is not calculating, my understanding of the underlying processing is that this is SAP Standard Behaviour.
To resolve this, do not default the Priority value, instead, select Subject and then Priority.
We had exactly the same issue on another system in recent months. I can see some reasons for SAP doing it this way...but it doesn't always give the user the right experience.
As for the second point, I'd recommend creating another thread for this.
Regards
Arden