All the three vehicles mentioned by you are outstanding in terms of mileage, performance and maintenance. However, the problem is that waiting period for Ford EcoSport is around 10-11 months whereas Amaze is available within 3-4 months. Hence, if you can wait for this long for both these cars, otherwise go for Maruti Swift Dzire. To draw a detailed comparison between these vehicles, kindly visit the below link: -
The engine noise is coming in the cabin because of poor cabin insulation and it depends on various things like gaps between panels and doors, material quality, etc. You need to get major changes in the interior for better insulation and we won't recommend that.
You should go for the fourth servicing despite the fact that you have not driven your car much. It is important that you go for regular servicing. Whether you want to go for wheel balancing should depend on if your car is bobbing while driving or it is not going in straight line.
The choice of the variant between diesel and petrol would depend on what would be your monthly run. If your monthly run is more than 1500 kms, you should go for the diesel variant else you should go for the petrol variant.