In my opinion...4k is useless unless you have the Computer power, video card and video editing program necessary to handle editing. Furthermore if you don't have a 4k TV/Monitor you can't experience the full resolution anyway.
I have the Computer above and film everything in 4k, and the only real benefit is that you have more color and resolution to work with....so that most people who still only have 1080p monitors can view the sharpest resolution possible while those with 4k monitors get the full experience.
As Mr Salty said, you don't need a pen... that is unless you have artistic abilities