The Build database and scan doesn't make it to 100%.
At some point, it crashes and I gotta start again

The stand alone version crashed a bit less
I'm running Windows 8 if that helps.
I don't know if this is the problem, but you can run it with "--rebuild" which will delete the database and start over from scratch (Bitcoin-Qt DB will still be there, so it will only take 1-2 hours to do a rebuild). I'm curious if doing a full rebuild fixes it for you. So far, I haven't seen any one need it yet, but if you have no other choice, you should try it.
Is this version already safe to use for managing (creating & broadcasting) offline transactions?
Or should I wait until the final release!?
It's safe to use for executing offline transactions. I'm just not 100% confident that the backups will be the same as the final version. I know it creates a frustrating dynamic, because I need people to help test the backups, but I have to tell them not to rely on them yet.