This is 7 travel days in total.

In addition, the pass for Italy only covers travel in Italy. Inbound/outbound journeys in your country of residence are only possible with a global pass. You can do this trip with a global pass for 7 days in 1 month.

il est pourtant indiqué que le pass permet d’entrer et de sortir de son payx, je ne crois pas avoir besoin du pass global pour cela?

ONLY, ONLY valid with the GLObal pass, which is valid in all of EURope. Many people ask about this, but at least in the english version it is very clearly explained. There should even be an explanation on the site of your SNCF somewhere.

You have to make the comparison what is cheapest yourself:

1.1 country IT AND 2 (probably not very cheap) tickets on that strike-prone SNCF from le Mans to and back from Milano. OR-perhaps even cheaper, on SNCF to Paris, cross city by metro and the rather new competition of TrenItalia to Milano.

2.global pass (can/should also be possible as paper pass be bought at the counter from SNCF in le Mans) PLUS the quite high supplements for the INTernat. TGV and for all the Frecce trains inside IT.
 Extra tip: it might be worthwhile to check to go direct from Venezia to Lecce (change Bologna and overnight train from there) and come back from there to Napoli-then Roma-Milano.

Merci beaucoup c’est très clair, je vais revoir mon parcours...je pense que je vais prendre des billets en france pour les trajets aller et retour, essayer de trouver avec des cartes avantage ou autre et puis prendre des billets version 1