Hi Tushar,
Based on the facts stated above, the asnwer to your questions is -
a - Yes. Selling of space over internet for advertisements is liable for tax under the category - ADVERTISEMENT-SALE OF SPACE OR TIME SERVICES.
There are a few conditions that you need to satisfy in order to claim your services as "export". However, since I do not know the exact business model, I am not commenting on your eligibility. One basic check is if you are earning in INR, then there is no question of it being an export. Having said that, earning in Forex is not the only condition. You have to satisfy all of them, which are -
a. the provider of service is located in the taxable territory
b. the recipient of service is located outside India
c. the service is not a service specified in the section 66D of the Act
d. the place of provision of the service is outside India
e. the payment for such service has been received by the provider of service in convertible foreign exchange; and
f. the provider of service and recipient of service are not merely establishment of a distinct person in accordance with item (b) of Explanation 2 of clause (44) of section 65B of the Act.
b - for obtaining registration, you need not have a shop & esatb. license.
All you need is a PAN card and an address proof.
If you are operating from a rented premise, you will require an NOC from the landlord in order to obtain the registration.
Hope this helps
Feel feel to write back for any clarifications.