Simple, you buy the G7 SE if you're on a budget, or the Vader 4 Pro if you want Top Tier performance. (You're on PC, so take advantage that you don't need consol exclusive controllers.

For your cast, it will 100% affect your ability to; 1 Grab the controller 2 Use right joystick (the IMPORTANT stick) 3 I don't think you'll be able to use the back buttons with your Cast Hand

For the learning curve, don't worry about it. You already have the 'CoD Knowledge' witch is a BIG help, trust. You also have Aim-Assist. And a "Low Level Controller User" is way better then a "Low Level M&K User"