How do Sub-Accounts work?

Hey,

I was just wondering how sub-accounts work on a PS3. Right now I have a North American (Canada) account but I wouldn't mind making an EU and *** account for early content and different content. I just have some questions:

Can I use the same playstation user account for each sub account?
If I download a Japanese demo, can I log off and play it on my NA account?
Is there any harm in creating a sub account, then deleting it?

Thanks!

P.S. If anyone has any tips on creating an EU/*** account (addresses and what not), if you would be so kind to PM me that'd be great. Thanks again!