How to select all party members in the tactical map

There's not - and you're not supposed to be able to until you get there. It's like it would be in person - you would have no way to know. The best I can suggest is to be careful and check the levels of creatures from a distance as you encounter them.

The location with the glowing green rift over it is the next story mission.

If there is more than one glowing green rift, you'll have to pick one and the other will go away, but the game will warn you about that.

The rest of the locations are more or less just open world exploration to get the resources needed for the story missions and so they can be done in any order. In fact they should all be done bits at a time as they have a wide variety of difficulty within them.