Don't think about horbito like an OS (yet), think about it like Google Drive on steroids.
Right now horbito is a great solution for teams, being able to work online with a much better user experience than old cloud (introducing windows and multitasking inside a website) and collaborating on real time while always being up to date on everything that's happening on your team thanks to Cosmos.
I really think Cosmos is a big revolution for teams because it's a well executed Yammer/Facebook for work due to being perfectly integrated with your workflow, you needn't stop work to report what your doing, as soon as you save you can share and post all the changes with your coworkers.
To me it seems that we don't really use our OS anymore, we do all our work online/cloud (Dropbox, Drive, Slack, Trello, Gmail...) so it makes sense to unify all our services into one place
Build a prototype and prove people are going to pay for your product. Having real customers desperate to use your solution is the best way to get into YC.
I don't think many people are going to buy your game because as you say it's very similar to Flappy Bird and there are thousands of Flappy Bird like games out there, yours is not much different from all of them.
Your game is not a clone like others but it's not different enough so people are going to pay 1€ (especially in Android) to play with it. Maybe if you make it free you can have a chance of getting people to try it and find out it's better than the other Flappy Bird games.
Why do you say the technical founder is always the CEO? The technical founder usually turns to be the CTO of the company. The CEO has to be someone who can stand being always on the spotlight, has to be really good doing networking and has to put up with constant stress from investors and running out of money. If you don't like to be in the spotlight and you're too much of a bad guy to be the face of the company then don't be.