Do I need a walk-in to use a modular closet system?

No. Most kits in this category, including the Rubbermaid Configurations and ClosetMaid modular units, are explicitly sized for reach-in closets between 4 and 8 feet wide. Larger walk-in setups typically combine two or more tower kits, like the multi-set Vomavex system, to span longer walls or wrap a corner.