based on my experience please find the answers to your question.
1. As you are employed and would have signed a NDA agreement with your present employer please go through your appointment letter, Offer letter or any other legal document signed with your employer. If it states anywhere that you cannot be employed with a competitor or same business, there is a issue. Ideally would suggest you to get the company registered in someone else name or any of your family member.
2. There are lot of paid database site such as dataguru.in, fundoodata etc. decision should be yours based on pricing and facility.
3. It varies from CA to CA in terms of pricing. Better to go for a LLP which is faster to register. A little google will help you with online service providers as well.
4. Ideally you should have a company space but as it is a new startup you can register with any virtual office / Shared facility which charge on a monthly rental. charges are nominal and again depends on the facilities being used.
Hope this helps you.