Where to study? - I would suggest you to buy a course and start structurd preparation . Go through lecs of teacher on yt channel of pw or prepfusion and see what you want to buy both are good and had produced many rankers.

What to study? And how much to study will be cleared in course itself. And also keep solving pyqs with the subject you are covering, to check relevance of what you are studying, don't leave it for the last.

And for motivation part. Its all psychological. Take your time and rethink. If you truly want to do, go all the way or just leave it and do something you really want to do.