I like to take my girlfriend to Versailles at the end of this month and we are planing to visit the Disneyland Paris (by train).
We start with Ligne L from Versailles, Rive Droite to La Défense and the with the RER A from La Défense to Marne-la-Vallée Chessy.
Is a Billet Ile-de-France Zone 1-5 ticket (per direction, per passenger) for 17,30 €uro right or do we need anything else to buy?
For single use Paris train tickets, there aren't zones per se, just prices based on starting and ending station.
The price I get from Paris train authority for the one-way Ile-de-France ticket from Versailles Rive-Droite to Marne La Vallee is 11.60€.
That billet origine-destination (ticket origin-destination) will get you from Versailles to Disneyland, one-way, no other tickets needed. You'll need to transfer from the Transilien L to RER A at La Defense, like you say.