Wa alaikum as salam bhai.
Basically you are talking about the w202 shape Mercedes Benz C class.
It is indeed one of my favourite models. Compact size, not very technical, easy to maintain, normal on fuel and still a Mercedes Benz 
I would suggest to stick with 98 and 99 models. Don't go below that. The shape is the same but the upper years had some technological upgrades that are really great.
Oil change requires synthetic oil. Different brands are available. You can go with any brand name that satisfies you. We use Meguin, a German brand. Costs 1000rs per liter. You will need around 5 liters. One oil change permits you to drive for 10k km. I, however change mine at 5k km.
Oil filter costs under 1k.
If you buy a good maintained car, you don't need to worry at all. These cars don't ask for maintenance so easily. Buy a badly maintained car and it means trouble.
No other maintenance except gear oil check once.
Auto tranny cars give an average of around 10km/l within city and up to 14km/l on highways depending upon driving style.
A good clean w203 will cost 10-12.5 lacs.
Will surely recommend one or two when you finalize your plan.
Regards
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