Three at most. One route planner (ABRP), one charger finder (PlugShare), and one roaming payment app (Shell Recharge, Chargemap, or Octopus Electroverse). You can add the dominant network's own app for the country you'll spend the most time in, which often gets you better pricing than roaming, but it's optional. More than that and you'll just confuse yourself at a charger when it counts.