mparadise I don't want to announce any pricing or time estimates before my base migration service is finished, which is still months away. When that's done I'll offer the base migration (only Flarum core features + PMs + uploads) as a small fixed price, and any custom migration needs can be added on top of it for a hourly fee. Feel free to contact me via email and provide the list of features you need that aren't part of the core Flarum for a rough estimate.
You can see a list of the available extensions here on the forum under the Extension tag, and on https://flagrow.io/extensions
While Flarum is pretty stable for production, we still officially say it's unstable because the Extension API is still being worked on, meaning third-party extensions will require further updates until stable to ensure compatibility. If you stick to trusted extensions that you know are under active support and can work with the Composer-based extension management, Flarum is fine for production already.