Can you carry someone while levitating?

The levitate spell targets "One creature or loose object of your choice that you can see within range . . . that weighs up to 500 pounds." If you’re airborne from casting levitate on yourself, could you then pick up another creature?

Is the answer different if your total weight is greater than or less than 500 pounds?

Would the weight of the second creature also need to fit within your carrying capacity as described in Can someone flying with winged boots/boots of flying carry someone?

If your passenger was unwilling, would you simply need to have successfully grappled them?