First: Thanks for loving the product
On your questions:
1. If you use the Veeam explorer for Exchange which most probably will be installed on a server (the same server as O365 backup runs on) you will have a 64-bit installation. So you would need to install a 64-bit Outlook on that server. If you export data to a PST (through that outlook) it will be able to be attached / read / opened by a office 32-bit client without any issues.
2. Uninstall O365 and the Veeam explorer. Then reinstall and you will be able to connect to that repository again. But please note (we love that you test the RC...) that we probably won't support an upgrade path from RC to GA. So please use for testing only at this moment
3. One of the things you can do is install this on a VM and then use Veeam Backup & Replication to backup the entire VM. Then you can backup to disk, rotating hard drives, tape, cloud provider and so on... This is also v1 of the solution and there is no real integration yet with our other solutions, but we certainly will look into this further with newer versions. Please let us know what your preference would be as we investigate all of the requests here very carefully