I would suggest you to look at the syllabus and past papers (last 3 years) of Zoology and Chemistry first. You have four years education in Zoology, utilize it if you can. Preparing a subject from the scratch is time taking exercise.

Regarding other subjects give some weightage to your area of interest along with syllabus. You should be able to make a decision after looking at past papers that you can tackle those questions or not.

Only you can decide your subjects. For instance you have asked about criminology and geography. Now I like geography and I would have chosen it no matter how low scoring it has been in the past because criminology is too boring for me and If I suggest you on the basis of that, how is it going to help you? That is just an example.

If someone knows you personally, your areas of interest and your background knowledge then that is a different story.