Cross-platform frameworks are just now becoming robust and stable enough to be a real concern. The most popular frameworks include React Native, Xamarin, and Ionic. The trade-offs are typically speed of development vs. flexibility and complexity. If you use a lot of platform-specific integrations like HealthKit or Google Fit, your best bet is React Native, as it spits out real native Java or Objective-C that you can further tweak or integrate. Xamarin or Ionic basically put wrappers around C# or HTML5, so your deep integrations are limited.

As far as the architect is involved, you're looking for someone who has experience in both Objective-C and Java, as well as the cross-platform language, whether it be Javascript or C#. This is because once you've built your cross-platform app, you still may have to write native libraries to integrate to the platform-specific features like HealthKit.

I can't speak for the education industry itself. You can post listings on Angelist or StackOverflow, but also scour LinkedIn to attempt to poach people. You have to assume a good architect is already well employed and isn't looking for work, so you're going to have to go out and find them.

I've ran into this problem before, in that good architects are really hard to find. It may be easier to hire a good mid-level developer, and train them in architecture. That basically means carving out 40-50% of their time to spend on architecture and research. They will then grow into that role in 6-12 months.

Hope this helps.