I work in a similar space here with frontofficepro dot com, although it doesn’t cover all the needed features and we only operate in USD and CAD right now.
For the amount of features I hope you have a large budget for a custom build or are flexible on what to include. As we looked into just adding on SMS texting for a customer but the cost to send texts though something like Twilio didn’t make it worth it - if you sent just 4 texts per a month to your 4,000 swimmers, that would cost $120 per month with Twilio (US pricing, not sure about HK)
Have you checked out Active Network yet? It’s a large company in the sport camp space and has a lot of different products from various companies they’ve acquired. EZ facility is another large player in this space