This depends on what do you want to achieve with email marketing. Depending on your budget, communication volume(current and estimated), features required, target audience, etc., there are different options. I will be happy to discuss this over a call with you.

Assuming you are talking about product detail pages, there are some conditions that need to be met about editing their content and owning pages depending on what exactly is the product that you want to sell. I will be happy to discuss this over a call.

There are many different kinds of investment that you might be looking for. I am afraid you will need to provide further details about your startup's niche, your investment goals, etc. before recommending any particular path. There are angel investors, there are VCs, etc. and also incubators / accelerators depending on what your business is and at which stage it is. Be sure to have a well-researched estimate of how much money you need to raise. I would be happy to discuss the possible options for you over a call.

I too have been thinking over this question since I am planning to sell online as well in the near future. However, there are several paths that can be taken in the world of digital marketing.
A lot more information would be needed about the exact product that you are trying to sell, e.g. by 'user', do you mean to refer to a paid customer or just an interested lead? What sort of skills do you have ready to be used in order to carry out the marketing plan? etc.
I would be glad to discuss this over a call. The world of digital marketing is vast and there are lots of innovative ways in which it can be explored, but in order to plan for the same, some information about the product itself is essential.

I am currently bootstrapping my startup and had spent some time a few months ago, trying to uncover whatever details I can about the very same question. Currently there are many grey areas in this field where laws have not yet been properly formulated in a comprehensive manner to take into account this new phenomenon in the world of funding. I am assuming you are asking this question for an unlisted, private limited company (meant for profit) and are specifically talking about equity-driven crowdfunding, and that you have registered your company following due procedures with the RoC.

There are certain issues with respect to FEMA and SEBI regulations, some clauses of the Indian Companies Act, etc. which affect your question's exact answer. I would be glad to discuss more details about the same over a call, and also in case my assumptions made above do not hold true.

Also, since you mention that you will be having overseas customers as well, don't forget to get an import-export code for the organisation, from the directorate general of foreign trade (if not done so already).