There's a lot you can do with MBBS, you can provide primary health care by opening your own clinic in a rural area or you can join government service and provide health care in villages at phc's . On serving rural areas for a certain period of time you'll also get reservation in pg. You can also go to research by joining icmr . There's ample scope you need not worry at all.

Now a days, as the number if disease is going on increasing, and the people are also more aware about their health. So now without Mbbs its hard to sustain good with your practise.
However you can get a decent amount though after mbbs only (nearly 80k to 1.3lacs per month,, in govt. Job only..)  ; but you may not find it intresting as you may not get new cases, nor more patients will come to you for treatment ..lots of other issues are also there.
So its better to do pg after mbbs. But if you are satisfied with mbbs only, and want to do govt. Job ,then its fine enough..

Good luck..

UPSC
RMO ship in any private hospital
Private practice
Salary-according to your efficiency
In these modern era of technology- degree is no the ultimate to earn.... it's totally on your capabilities,hard work and passion