As AK1311 posted it is very important to have experience in dairy farming or else you will make huge loss.
Keeping any animal always tied in a shed is not a healthy practice(dairy farmers have no other option). So you will need a well experienced vet who is available for your cows.
Then feed is another important factor. Some dairy in my locality use malt(beer waste) as feed, along with few other feed.
Dairying is not a one man army. You will need some one to replace you at times when you are not around. Keeping full time Labor is not a ideal option(Charges and will they treat your cows well?)
Peak milking is just for 3 months after birth of calf, after which it starts to lower. Say if you inseminated the cow after six months of milking, From there on you will be able to milk cow for another 3 months for most cows. In some cases it may extent for 6 months or more.
Ideally you will have to feed a cow for 6 months with out any income from her(dry period).
Most dairy farmers keep 10 cows, 5 milking and another 5 should be ready when the earlier 5 go dry.
One dairy farmer near my locality has stopped his dairy and drives a auto now. In Kerala most dairy farmers are making loss or are struggling. I believe it is the same in most part of India. Only big players are holding back with perks and subsidies from governments.
Not just that you need lot of water supply to keep the shed, cows and other equipment clean.
Dairy is not a easy task. Lot of things have to be considered before getting into it.
hope this gives you some idea. let me know if you need more info.