Welcome to the Microsoft Teams Community!

Thanks for using Microsoft Teams, Julien! 1. If the default document library (I'm not 100% certain what you mean by that) is an ordinary SharePoint document site, you will be able to add that to a team shortly. We couldn't quite fit it in before today's release. 2. You can't take an existing Planner tab and show it within Teams, but we've heard a number of comments on this and we're definitely considering it. 3. When you create a new Planner tab, it's associated with the same group that's associated with the team (every team in Microsoft Team is associated with an O365 Group. While the Planner interface only supports one planner page per group, there's really no limit, so that's what we are taking advantage of. We are working with the Planner team to eliminate this admittedly confusing situation.