Can this OS be used as a daily driver and is it possible to get Play Store running?

Yes, i'm using this since yesterday and i haven't noticed anything wrong so far. I would advise you to make a clean install. You might enconter issues when connecting to your google account, but removing and re-adding the google account worked for me. It seems faster than previous version, that's probably also because i restored it to factory settings. Battery seems to last a bit longer also, with Flyme 5. Good luck installing it!

After installing this will i be able to upgrade to the official release when it's available?

Thank you for your post ultrametric.  Everything works great.
When the stable version will be realese.  Will be available more language.? For example spanish.  

I upgraded to the beta just now,  its awesome,  still no bugs found

I had the whatsapp  notifications delay in the previous version of flyme 4, I've been using flyme 5 beta for about 12 hours now,  no problems yet,  and it seems my battery drain got slower than before,  I'm happy at the moment

Hey guys!! I have been using flyme 5 beta since last week. It is awesome. Though i found some bugs which i would like to share and hoping to be resolved in the next update.

1. Notification issues. I am not receiving any notifications  other than whatsapp and gmail. Sometimes rarely receiving fb notifications.
2. Sometimes notification bar acts sluggish when receiving multiple notifications at a time.
3. Also i feel multi window is not useful unless you add some gud apps like watsapp, fb, YouTube, gmail, instagram, browser and many social applications.

Hope you would consider my above points and make flyme 5, a stable version. Thank you