IEC necessary for selling products online to international customers

As per the latest information available and Govt circulars in the matter you need not to register for IEC (Import Export Code) for exporting the goods or merchandise from India to outside country. But you have to get GST registration which you are already processing. Once you are registered for GST then for exporting the goods your PAN number would be taken in place of IEC code and that would serve the purpose.

Earlier IEC registration (IEC is a 10 digit life time code for an individual or company) was mandatory and was to be got from the office of DGFT (Director General of Foreign Trade) which used to issue an IEC code to the exporter. One can still apply for it but under GST regime as the PAN number is doing the same thing and serving the purpose, it is not required.

The full form of IED is not mentioned anywhere in the question. In the first answer, IEC is taken in place of IED. Thinking this IEC, I am giving the following answer.

IEC is not required for service exporters for other countries. But if you want to avail benefits under foreign trade policy. GST is mandatory. It is mandatory for all other exports and imports.

IEC code will be the same as of PAN these days. But DGFT will issue this code separately if you apply for it in the prescribed application.

IEC code is to be taken by all organisations which are HUF, proprietorship, private, partnership, limited, Trusts, society and LLPs,

The following are exempted from obtaining Importer - Exporter Code (IEC) number:

1. Importers covered by clause 3 (1) [except sub-clauses (e) and (l)] and exporters covered by clause 3(2) [except sub-clauses (i) and (k)] of the Foreign Trade (Exemption from application of Rules in certain cases) Order, 1993.
Ministries/Departments of the Central or State Government.
2. Persons importing or exporting goods for personal use. They should not be connected with trade or manufacture or agriculture.
3. Persons importing/exporting goods from/to Nepal provided the CIF value of a single consignment will be less than Rs.25,000.
4. Persons importing/exporting goods from/to Myanmar through Indo-Myanmar border. But CIF value of a single consignment should be less than Rs.25,000.

Yes, IEC or Import Export Code is a compulsory compliance in order to send any product out of India for commercial purpose.

As you mentioned that you will be on boarding ETSY and Amazon Global so once you start your registration there, these sites itself will ask for your IEC code and you will not be able to complete the registration without the IEC code.

Nowadays IEC can be easily obtained and your PAN number itself is treated as IEC.

So, before registering on Amazon, ETSY or other portal IEC is must. Whenever you will send an international courier through FedEx, Blue dart or other logistics they will ask for your IEC code and Form 1 that you will have to comply in order to send the parcel outside India

For rest of the compliance I believe you are already aware so, I won't dwell into them .
So, go ahead and make the most of your business on international platform.