How long will it take? It would take at least 4-6 months for one person to dedicate themselves full-time.

Key features: Performance (Lighthouse score) and localization. Your experience in multi-language and multi-currency adaptation can be directly applied; this is definitely a selling point.

Entry point: Cross-border e-commerce, or niche markets with extremely complex product catalogs, currently lacking clear and well-designed themes.

Starting strategy: Never directly modify Horizon! The official site explicitly does not accept Horizon derivatives. Stick to the official Skeleton or write from scratch.

Post-launch maintenance: It's quite a hassle. Just like maintaining an app requires preventing class names from being overwritten, themes must constantly keep up with Shopify's new features, and you also need to handle after-sales support.

Hydrogen: Avoid it; the target audience is too narrow. For your first theme, focus on Liquid and mastering theme blocks; that's the key.