Hello -
These are a lot of very good questions - however, I'm afraid responding to them in a satisfactory manner is beyond the purpose of this discussion forum.
As a first step I would suggest to look up the online help documents for High-Perfromance Forecasting (the forecasting engine of Forecast Studio) which will provide you with lots of information about the default settings of each of the options.
You might want to consider to contact your SAS representative and discuss with him/her the possibilties of adressing your questions in person.
Thanks!
Udo