Learning bollywood songs alone will not be good for you. It will not help you sustain in bollywood for a long time. Learning classical music will make your base strong. It is the best approach. So I would advise you to learn classical music rather than going for bollywood songs.
I agree.. Bollywood songs are the final thing that you will be to sing. You need to perfect your singing in all ragas which is possible only through classical singing..
If you want to sustain yourself in this industry, then you need to work hard. You have to do daily riyaaz. Now a days there are many singers who are without any formal training but they disappear after giving one hit and can't sustain themselves for long. You need to get formal training to know the finer nuances.
Working hard is necessary if you want to make it as a professional in this field. There are a lot of singers working nowadays who haven't had any training but manage to have one big hit before they fade away. amanda the adventurer