Can I run a single Magento store for NL + BE + DE?

Yes — this is one of Magento’s strongest features. We typically architect it as 1 website → 3 stores (NL, BE, DE) → 3 store-views with a shared catalogue and shared customers, but per-store BTW rates, currencies (all EUR but separate tax-config), languages (Nederlands / Frans-Nederlands / Deutsch), payment methods (iDEAL for NL / Bancontact for BE / Klarna + Sofort for DE), and shipping carriers (PostNL for NL / bpost for BE / DHL for DE). Hreflang per store-view, separate sitemaps, separate Google Search Console properties. Same Magento backend, ~30% lower TCO than running three separate Magento installations.