Here are some facts that may help you:
Some jurisdictions will not let you get a name or form an entity until you are actually ready to do business. The Indian government has published some guidance on this here. If in doubt, you should contact a lawyer experienced in working with small businesses in India. If you just want to get a name, then (I believe) the form you need is this one. You may also need to register a trade mark or service mark. In most common-law jurisdictions, this is just as important (if not more so) than the name that you give the business entity itself.
You can register a domain name anytime, as long as it's not part of a restricted top-level domain. If you are permitted to register the domain you want without forming a business, then you can register it now and transfer the name to the business later.