Learn Russian: Почему вы уезжаете так рано?

Уезжаете specifically means leaving by some form of transport (car, train, etc.), since it is built from the verb for riding/driving. Уходите means leaving on foot. If you are asking guests why they are walking out of your house, you would use уходите.

Why is the verb уезжаете (imperfective) used here instead of its perfective partner уедете?

The sentence is asking about an action happening in the present ("are leaving" right now), so it requires the imperfective aspect. In Russian, perfective verbs cannot be used in the present tense. If you used the perfective form уедете, it would automatically become the future tense, changing the meaning to "Why will you leave so early?"

Why does уезжаете look so different from the basic motion verbs ехать and ездить?

Prefixed verbs of motion often use slightly different stems. To make imperfective verbs for "going by vehicle" with prefixes (like у- meaning "away"), Russian doesn't attach the prefix to ездить. Instead, it uses a special stem: -езжать. So, "to be leaving by vehicle" becomes уезжать.

Why is "so" translated as так here instead of такой?