Yes, you can edit chat settings for each user.
To do so,
1. Go to 'All clients' in the client section in the main menu panel.
2. Click on the name of the user whose chat settings you want to edit.
3. Go to the information page of that client and click on the Settings button on the top right of the page.
4. You can easily enable or disable chat from there. In case you wish to do so while assigning the plan for the first time, you can simply go to the settings button and make the edits.