Are important questions enough for intermediate IPE?

No, If you want good marks in Intermediate IPE (Board Exams), you cannot just study important questions. Important questions can help you narrow down your study focus and point you to likely areas of questioning, but the board can pull questions from anywhere in the syllabus. Hence, my advice is to

No, relying only on the so-called important questions won't carry you far in Intermediate IPE. Sure, those questions let you brush past key topics in a hurry before the exam, but the IPE still tests the whole syllabus. 
To really score well:
First, work through the full textbook so every concept sits