I can mention all these facts in a covering letter, is that enough to
convince the embassy or what more can I do ?
This has already been answered by Gayot Fow regarding what documents to produce if working as a freelancer:
What to write in visa application form and what documents to submit as an unregistered freelancer?
Simply follow the above guideline if you working as a unregistered freelancer.
Moreover if you have a registered company under your name, you can provide the following documents with your application:
- Company registration certificate with relevant authorities plus copy
of your business license
- Company bank statement of the latest 6 months plus maintenance certificate
- Income Tax Return (last 2 to 3 years)
There is absolutely nothing wrong to apply as a freelancer, the only concern is you need to convince the visa officer that you earned all this money lawfully in India.
I am looking for multiple entry short stay of 90 days, although in
reality I would be staying in Schengen more like couple of weeks at
First of all embassy/consulate would issue a multiple entry Schengen visa only if you are planning to enter 2 or more times in Schengen countries. You explicitly stated that you are intending to stay in Schengen countries for acouple of weeks at the most, therefore you simply need to apply for a couple of weeks provided you have complete hotel booking, travel insurance, itinerary and all the requirements with your visa application. Also you should simply request 2 weeks duration in your visa application form.
Moreover if you are traveling in and out of Schengen countries (visiting non Schengen countries as well in your itinerary) then it would be feasible to apply for a multiple entry Schengen visa otherwise just simply apply for single entry Schengen visa. Similarly if you have previously visited Schengen countries last few years regularly, the Embassy/Consulate might issue you longer multiple entry Schengen visa depending on your application and situation.
Therefore the best practice is stick to your itinerary and apply for 2 weeks Schenegn visa instead of 90 days multiple entry Schengen visa.