Party members leveling and importance

[Ohm]

How does the leveling for your teammates work in this game? Is it similar to Mass Effect where you can just set it on auto-leveling and consentrate/care only about your own characters progress?

Is it also possible as a challange to complete the game on your own without a party?

And a last one; how paced is the combat? (to compare the combat in Dragon Ages is to slow, Mass effect had a good speed for me)

thanks