I'm beginning a project using Microsoft Bot Framework with Microsoft Teams. SDK V4 is already available but I saw that Teams uses V3 of the SDK only. Is there a way to add a v4 Bot to Teams? or I can just use v3?
You can use bot created with v4 SDK (Bot Builder SDK) in Teams, there is no problem around that.
As the comments mention, there are even official packages provided to use with this v4 to get more details about Teams, here: https://github.com/OfficeDev/BotBuilder-MicrosoftTeams-dotnet It is not mandatory to use them to get a v4 bot in Teams, they provide additional functionalities.
If your question is about publishing a bot, the guidelines are provided in the documentation, here: https://learn.microsoft.com/en-us/microsoftteams/platform/publishing/apps-publish