Hi there !

- how do I set password for this wallet?
You can't atm, but it's planned.

- location/folder where files are stored on my phone (is it just wallet.dat or any other files)?
if you have root access: /data/data/net.vanillacoin.vanillacoin/
auto-timestamped wallet backup is done during file creation, you can find it in the /sdcard/ folder.

- how do I copy/paste address if I want to sent from my PC to my phone wallet?
From the QRCode, you can use http://zxing.org/w/decode.jspx to decode a screenshot of the mobile wallet's QRCode
More features to like Address Sharing are ready to merge from the dev branch.

- can I add more addresses or just 1 (default) possible?
Not atm, so only 1 address by mobile wallet (planned, but no eta)

- how do I "open" wallet for staking?
Just open the Vanillacoin app & let it run in Background

Jump on iRC if you need help.

Have a good n8/day !