The OFFICial rule is that you have to '’use'’ country of residence, whichy is where you have stayed the last 6 monthes and are registrated in the public administration. However, some countries do not even have such a registration system proper. But the rules were made for EURopeans and here anyone has.

EU rail as such is better value as INTERrail-because it does not have the '’only 1 trip OUT and IN'’ in your own country. Prices hardly differ.

Also double check if a pass is even worthwhile for just these trips-this will also depend on how many breaks you intend to make and/or side-excursion trips. There is now a direct overnight train from P to Wien=Vienna and for local travel, unavoidable with your plans, in FR and even more in ES-on TGV and AVE Hi-Speed trains, cumbersome and sometimes very hard to get and costing extra REServations need to be made.

Thanks for responding. In your opinion would it be cheaper to by the ticket from Paris to Vienna directly for the overnight train? - does it come to the same buying the Eurrail for 4 days and buy the extra reservation fee? Would really like to know what are you thinking about it. We never have used Eurrail before. 

The reservations can be quite expensive Reservations for Eurail & Interrail on Nightjet Paris - Vienna

Even the trains from/to Mardrid needs a reservation and as there is no direct train from Paris you need to change and because of that need two reservations

Paris - Barcelona (up to 56€on top just limited seats for Railpassuser)
Barcelona - Mardrid (usually 15-25€) 
same backwards.

There used to operate a TGV/AVE from Marseille to Mardrid
means Vienna - Frankfurt - Marseille in one day and then nextday Marseille to Mardrid.
Frankfurt - Marseille (17€ in 2nd Class)
Marseille - Mardrid (up to 56€ like Paris Barcelona)