Hi Nitin,
1. You can create custom Code List (drop downs) in SDK.
2. You can bind the Enabled property of a field on UI with indicator (Yes, No)
(Property->Behavior -> Enabled -> select Advanced. Bind with the indicator from datamodel)
3. Refresh? Do you mean to initialize the fields?
You can write ABSL in aftermodify event. (there is a built-in function Clear()).
4. I dont know what you meant. 
Please refer to to 2.
Hope this helps.
Fred