Since the mouse isn't really used when navigating through the world, simply capturing the mouse movements without asking to click would go a long way making gameplay go smoother :)
Apart from mobile games, it is unusual to use a press and release type of input on top of movement to rotate the camera
On the combat side, since the player needs to constantly moving, having abilities tied to E and R require the player to use his middle finger or index. You could bind it to C/V and spacebar for example to require instead a thumb movement and not hinder the fingers used to move :)