I'd frame out about 200-400 sq ft with an office, lounge, kitchenette, bathroom or some combo there of. Be really nice to have an office to organize your projects from. Storage space above. Put the lounge or office right next to the OHD w a window to let in light.
Leave the rest of it open and let tool placement define the rest of the layout.
All that plus how do you envision using the space is really needed to help with design ideas.