Select iOS Tablet for 3D Modeling

I’m ready to purchase a tablet dedicated to drawing-focused 3D modeling and want an expert to pin down the exact iPad model and accessory set that will give me the best balance of power, screen fidelity, and future-proofing... (Budget: $250 - $750 USD, Jobs: 3D Design, 3D Graphic Design, 3D Modelling, 3D Rendering, Digital Art, iOS Development, iPhone, Mobile App Development)