Realization about your goal is the most important thing that motivates to get ready for action.
Looking at your circumstances, it is little challenging but, with sincere efforts, you can convert your dreams in to reality.
As you mentioned about CSAT, first be clear about the complete exam-plan and related requirements at each stage of the examination. Preparing only with Preliminary examination in mind is not going to bear fruits.
Still, you have time to prepare and should plan your foray at least one year in advance so that your preparation is as per UPSC expectations and you emerge winner in your first attempt.
Your academics support your decision and even, choosing optional subject should not be a major issue as Psychology is one of the most popular optional subjects.
Newspaper reading is a must and cultivate habit of reading at least two newspapers daily.
We suggest begin your preparation with NCERT books for laying a solid foundation and then, move on to specific subject books. This will help in better understanding and as you advance, you will understand the value. Even, while reading newspapers, clarity about the basics would be of great help.
Commence preparation adopting integrated approach (Main Examination oriented) and aim to cover General studies as well as optional subject preparation in next six months or so.
While preparation, your Preliminary Examination Paper I preparation almost get done and for Paper II (Aptitude Test) you need to brush up your knowledge relating to mathematical/reasoning/linguistic skills and that should not be a problem. You can learn all these as mood-changing activities during preparation for General studies and optional subject.
Despite the fact that your child would take lot of your time and attention, you can plan your daily routine keeping in mind all engagements.
Continue preparation and keep moving slowly towards your destination.
All the best!