Oftentimes the "best" solution is what would be most familiar and usability by the person/people build and supporting the application. In addition to what some of the other responses post, I would also offer that "best" server solutions in this instance may also include how best to scale storage costs and scale users so the application doesn't experience any lag or latency issues with accessing and streaming content. Part of this too will depend on your growth plan and how quickly you expect to need to scale the platform.

Regarding programming languages, there are really only 2 considerations you have to make: 1) for the back-end, there are a myriad of options you can use (again, I would make the focus using a language that is scalable in terms of your ability to recruit talent to build out and support it instead of necessarily advocating Ruby on Rails over say PHP or Python). 2) for the front-end, the only consideration to make for native applications would be utilizing Objective C or Swift (or a combo of both) for iOS. Swift is the newer language and rolled out by Apple, however they will likely never (or not for a long time) move away from allowing Objective C such a huge % of the current apps in market are based in it. So, I would also default this response to a consideration of who you are recruiting to build it versus optimal coding of one language versus another.

There are however some generally steps you can take for your tech team to give them ideas on your blueprint and know where to start for recruitment. So from that standpoint, building a technical specifications document outlining wireframes/front-end and also back-end requirements may be helpful towards organizing your thoughts. Feel free to reach out if I can answer any other questions or if you want to discuss how to build out a technical spec doc.