How do I handle the 80% cross-border traffic to NL + FR + DE?

Belgian e-commerce is uniquely cross-border-heavy, ~80% of Belgian online shoppers buy from foreign stores (mostly NL, FR, DE), and many Belgian merchants serve those neighbours back. The Magento setup:

• Multi-region storefront, one Magento install, multiple websites or store views: be_nl / be_fr / be_de plus optionally nl_NL for Netherlands shoppers, fr_FR for France, de_DE for Germany. Shared catalogue, separate URLs (yourbrand.be / yourbrand.nl / yourbrand.fr / yourbrand.de).
• Per-country VAT, BE 21%, NL 21%, FR 20%, DE 19%. Each with its own reduced rates. OSS (One-Stop-Shop) for distance-selling thresholds.
• Per-country payments, BE: Bancontact / Payconiq / KBC. NL: iDEAL. FR: Cartes Bancaires (CB). DE: SEPA Direct Debit / Klarna / Sofort. We layer them per store via Mollie + Stripe + Adyen.
• Per-country shipping, bpost for BE, PostNL for NL, La Poste / Mondial Relay for FR, DHL / Hermes for DE. Mondial Relay also works BE + FR pickup-points.
• Per-country legal pages, Algemene Voorwaarden (NL), Conditions générales (FR), AGB (DE), and BE-equivalents per language.
• Currency, all EUR, no FX rebuild needed.