(Almost) All Answers of the devs in the "HayliNic" Twitch Chat self.Overwatch
I didn't considered double and off-topic question. Maybe I missed some answers, sorry for that.
All answers listed here were given official by the devs.
Q: Will there be many changes between this version being shown and the beta version?
A: Probably! This version you're watching now is what we call "Show Mode." so a lot of systems and settings are disabled (that will be available for beta).
Q: The card system after the end of the game, does it have any effect on player progression or rewards?
A: Not currently! We'll see how feedback goes in beta, though. 
Q: What is that bar underneath the Health bar?
A: Is our current version of what we call our "on fire bar" (super technical term). If you start to pose enough of a threat, your portrait will catch on fire in the score screen and indicate to the other team that you're dangerous and probably should be murdered. 
Q: Have you guys given any thought to player cosmetics? I saw you just mentioned portrait borders and what not, but what about skins or gear?
A: That's definitely be one of THE most popular requests we've had (skins). We think it could be a cool idea!
Q: How long will the Beta last?
A: Hard to say. It depends on how player feedback goes, as well as how our stress tests go.
Q: Do the characters have infinite ammo? It seems like her secondary ammo count isn't going down
A: Infinite ammo in that you don't have to pick up ammo as you go. You will need to reload periodically, however; the frequency depends on the hero and their gun's magazine size.
Q: Can we expect a founders pack like we did for the HoTS beta?
A: We haven't announced our business model yet.
Q: No beta for eu, why?
A: We're hoping to launch beta in our Europe and Asia gameplay regions are soon as possible. We're still working to get those regions ready!
Q: Will there be hero changing in the competive mode(s)?
A: We'd like to see how beta goes. Hero switching is a pretty core mechanic of the game and we want to see how the game fairs with a larger audience before we start adding any rules. (We'd like to avoid adding rules if possible. Overwatch is kind of defined by its "unbound" nature.)
Q: Has Blizz said if they are going to announce anymore heroes before the beta starts?
A: Blizzard has not said! However, the content you're seeing today (heroes and maps) will be what you'll see in beta when it launches!
Q: Is there a single player mode?
A: There isn't. We no plans for a single-player mode for Overwatch right now. It definitely is a multiplayer, PVP focus.
Q: Will we get the Junkrat and Roadhog gameplay previews?
A: We're more focused on getting the game ready for beta, but we hope to provide those gameplay previews as soon as possible.
Q: Is there controller support or is it better to play it with mouse + keyboard?
A: We're working to get controller support. Whether its better to play with one or the other is completely up to the individual player.
Q: How long is the average overwatch match ?
A: On the teams and how well matched they are. Typical matches last between 10 and 15 minutes, though.
Q: what is the min requirements for this baby?
A: Still working those out! We hope to share current min specs when beta begins.
Q: Can you get "kill streaks" when you get assist "eliminations?" That seems.... pretty lame.
A: It's a team game, so kill streaks do get awarded with assists as well. Your scoreboard will differentiate between eliminations (kills + assists) and killing blows, though.
And here 2 Answers where I missed the questions:
A: There definitely are ways to customize your settings (keybindings, FOV, mouse sensitivity, etc). Those aren't really available in this "Show Mode," but will be available in the normal game.
A: For cosmetics, we are experimenting with a progression system that does award cosmetics like hero portrait borders. Our progression system is still in its infancy, though! You can see the beginnings of it here.
