I work with mostly 3D modeling, VFX and Video Editing mostly but sometimes client require us to sketch, draw and make digital art for them to incorporate into the final product. Laptops are definitely out of the question, the portability is okay but I don't understand why you would need one when you'll be working at home or an office most of the time. (they cost more, you cannot upgrade them, are sluggish on long sessions and just suck in general, imo)
SSD -- get the biggest you can afford.
CPU -- i5 /i7 is fine as long as it's mostly digital art.
RAM -- I personally always suggest 16GB if you're going to work with Photoshop, SAI or any other programs like that. It gets really slow when those projects start to become big.
GPU -- you need a dedicated graphic card for sure. You want to work quickly and get shit done. Don't cut around corners.
As far as a mouse goes, I just use my XP-PEN Deco 03 ( xp-pen.com/product/89.html ) Graphics Tablet when doing digital art, no point in using a mouse to be honest.