The biggest challenge in the dairy farming line is that those who are venturing into this field are mostly new comers. They have limited knowledge about cows, breeds,yield and availability of the cows and they fall prey to brokers and cow sellers. Indigenous breed has got better immunity compared to Cross bred cows but they yield little low, may be with better fat percentage in milk.
Design your cow shed, plan for providing water for cows 24 x 7, give them good housing with comfort, if possible give partitions between cows (locally designed ones), put cow mats if your budget permits you to. You can add this later too.
First of all, you are starting this venture with your hard earned money, right. Then you must keep cows which will give you more milk. Forget about getting indigenous breeds from Northern and Western part of India, spending too much on transportation. You can think of that when you start making money from the farm. In Karnataka, you will see mostly Holstein Fresian breed (Kolar in karnataka / Krishnagiri in TN). Please do not experiment with your money. Go for cows which will give you more milk and of course -good returns . Go for other money earning devices like Vermi composting using earthworms which will fetch you good money by selling it for vegetable cultivation areas, coconut, arecanut or any agricultural farm, produce organic manure by using the green waste, cow feed waste and dung. Pack it in 1,2,5 kg packs and sell it.
All the best for your venture.