Hi Taras,
There are some limitation on windows azure
VM Role: currently, the only supported os are windows 2008r2; all the data stored in vm role is not secured, it's possible that the vm role instance is broken and be reimaged automaticly, in this case, the data stored in vm role would be losted.
For billing question, the VM role is charged by computing hours, I suggest you contacting
windows azure billing and subscription manangement support to get deails info
http://www.microsoft.com/windowsazure/support/
Just found this thread, it may be useful to you
http://social.msdn.microsoft.com/Forums/en-US/windowsazurepurchasing/thread/01de73bb-053e-4179-8078-39f465eb3651
Thanks,
Mog Liang