iOS & Android Fitness App Development

Hey there, I need a mobile app developed for my business. It's a fitness course website based on Wordpress where we sell a fitness course to our audience. To have a better User Experience for our customers we would like to get an app in our portfolio so the user can access the content easily on the run, in the gym or anywhere they like. Also the workout plans should be easier accessible. The design were done by myself and an overview (as a pdf) is in the attachment. Now let's get to the functionality of the app. It's all basics things I guess. So my website runs on Wordpress and which is a major point for the app is that the users can login with the same credentials in the app as they do on the website (WP REST API). Also our course uses content dripping. When a user registers the content of lesson 2 will be released after 1 week, lesson 3 after 2 weeks and so on. It's a video based course and we would like to have a progressbar under each video of a lesson and also the videos should be greyed out or something to show the user they already watched that video. The app should show pdfs and in every lesson 5 recipes are included and need to be shown. (You can see it in the design). For my understanding building this app in react native is the best way. So one app is build and can run on ios, android and so on. But if I'm wrong, correct me. :-) If you are interested please contact me and if the price is too low you also can tell me your price. It would be also nice to get an average work time - so how long does it take you to build this app. Thanks in advance to all. Kind regards, Max