Mouse Click Based Movement/Actions & 2D Sprite Rotation in 3D Space

I have two questions. How can I make it so that when the player clicks the ground, it then moves there. What about if it is an enemy the player clicked? How can I make the player in that case first move next to the enemy, then proceed to attack it. Could the same method be used for several other things for example to trigger a conversation with an NPC? I guess you could use RuneScape as an example here.

Second question regards use of 2D sprites in 3D space. I think we could use RuneScape (the old one) as well here, I'll leave a image or two at the bottom. The player has four/eight different graphics, each for a different direction, can't even remember that anymore and can't check YouTube now. But the player is always shown as a 2D graphic, even if he would rotate the camera 90 degrees with arrow keys. How can that be made? Is it possible to utilize Unity's 2D functions here (When they'll be availiable or beta build)?

I prefer C#.

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NOTE: If there is any problem with the mention of 2D beta build, please contact me and/or remove the post.

EDIT: What's wrong with the images? They work fine in the preview.