Given different sources of income including W2, dividends and self employment and all self employment income was on IL, then 100% of the 1/2 self employment deduction should be allowed or just the percentage of the SE income to the overall income ? Same question for line 28 (self employed SEP, SIMPLE etc) ?
Yes. The 1/2 Self-Employment deduction is a direct function of your IL Self-Employment as is the Line 28 SEP deduction.
If you have additional questions or details regarding this, please feel free to post in the comments for further clarification.