Create 3D Mall Environment in Unity

I would like to start with building the entire 3D shopping mall environment as a standalone Unity project (without any app integration for now). Below are the full details and scope:
General Mall Requirements
• Create a full 3D mall environment, optimized for mobile (Android & iOS).
• The mall should include:
• Multiple floors (2–3 floors as a start).
• Corridors and main hallways with open walking areas.
• 20–30 store spaces distributed throughout the mall (interiors can be placeholders for now).
• Main entrance area, with a welcoming lobby and clear navigation signs.
• Decorative elements (lights, plants, benches, banners).
Store Spaces
• Each store should have:
• Basic interior layout (walls, floor, shelves placeholders).
• Space for product shelves and display areas.
• Doors or transparent entrances.
Movement & Avatar
• Enable free walk movement inside the mall (first-person or third-person view as you suggest).
• Prepare placeholder avatar support, so the user can move as an avatar later.
Design Style
• Modern, luxurious mall style.
• Clean lighting, bright and attractive look.
• Add escalators or elevators between floors.
• Basic interactive elements (like opening doors, rotating ads).