The Netherlands should be your main part of your Schengen visit, but it does not need to be your entry point, it does not need to be your exit point and it does not even have to be your longest stay.
It will be easier if your stay in the Netherlands is longer than any other, as that is easier to proof than the main reason to visit.
When you enter the ...
First of all, I think the person you are speaking to is a bit lost, as the list you opened is:
List of third states the citizens whose nationals, holders of diplomatic, service/official and special passports are exempt from the visa requirement in order to enter Romania
People with visas from these countries are exempt from an invitation
On the ...
For Russia: an invitation is mandatory, but it is given to you by the hotel or the travel agency you book the travel, if you are staying for tourism. It is very easy to get, and as far I know, it is not really checked after you get it.
[In my case, I had to change completely the plans, and cancel a tour, but I did a much shorter tourist travel in Russia ...