It may help, but the panel still consumes more power than an FHD panel - and you may find the image less than satisfactory.
If you want active pen support, that's the 9575 model - not the 9570, which does not support an active pen.
This has come up before. It may be some of these shipped with digitizers - but it's not a standard feature, so unless you get to buy somewhere you can try the unit you want to purchase, don't count on using a pen with the system.
Dell will not guarantee pen compatibility with this model.
The Pens will usually work with compatible 2-in-1 systems. Logically, this makes sense because you can use a screen configuration which makes it easy to adjust your hand position for writing or drawing.
I feel the best way to know is to check the product sales page and look in the compatible devices section. But it can be confusing when the 9570 is a normal laptop but the 9575 is a 2-in-1.
As far as the battery life, my Inspiron 15 7567 4K display seems to have a normal battery life. But you are the only one that can judge how the battery life fits your application of the system.
I will tell you running a game in 4K resolution does take a severe toll on the battery.