While a person who has done med school from the US has to clear an exam by Medical Council of India, the doctors who are board certified in Medicine, Pediatrics, etc are exempt from it. But the MCI keeps on changing its stance with great regularity so things can change by the time you reach that stage.
As for the money, it is highly variable. Patients, especially the financially better off ones, would love to visit a US trained doctor and pay more, so you're likely to be accepted by a higher paying private hospital. Another major factor is that whether you are planning to be ethical in your practice. If yes, then your salary could take a slight hit, since you wouldn't be ordering unnecessary tests or medicines, decreasing your hospital's revenue. Considering all the variables, some of which neither you nor I can fully understand, you should be earning pretty well in India, though it might fall short if you directly convert it into dollars or have very high expectations. I wont put a numerical figure, since if you do come to India, it will be years from now.