1) you can start your own business in same field after leaving your job

2) It is a general principle of the common law that a person is entitled to exercise his lawful trade or calling as and when he wills and the law has always regarded jealously and interference with trade, even at the risk of interference with freedom of contract as it is public policy to oppose all restraints upon liberty of individual action which are injuries to the interests of the State.

3) section 27 of indian contract act Agreement in restraint of trade void.--

Every agreement by which anyone is restrained from exercising a lawful profession, trade or business of any kind, is to that extent void.

Yes, there is no bar to make the business of similar nature in which your ex-employer was dealing with.

However there is exception . if at the time of your employment you had signed any bond or agreement that on termination of service you can not run similar nature of business,

However such term/clause can be challenged in court if it is found to be unjust, arbitrary and unconscionable.

You have to tender your resignation following the terms and conditions of employment or appointment letter properly, the conditions if any in it restricting you from professing the same business with your company's competitor is to be taken care of because it may affect the previous employer's business in the market hence the restrictive clause has been included in the letter of appointment or employment. You may consult a local lawyer with the relevant papers and take his decision before leaping into the new venture as desired by you so that you can be prepared for legal proceedings if any that may arise due to your proposed act.

Yes you can unless the employment agreement states anything to the contrary. Principles of good faith might prevail but still it will be a difficult case to prove for the employer.

YES, YOU CAN.

Yes why not. All citizens are given the right to practice any profession or to carry on any occupation, trade or business.