All servers on your account are billed hourly up to the monthly rate cap. The hourly rate is determined by dividing the monthly rate by 720 hours (28 days). If your server is online for more than 720 hours in a calendar month, you will only be billed the monthly rate. Accumulated charges are invoiced to your account on the 1st of every month.
Yes, instances in a stopped state continue to reserve dedicated system resources (RAM, SSD storage, IP aliases, CPU) and therefore incur charges until you destroy the instance. If you wish to no longer accumulate charges for a virtual machine, please use the DESTROY button in the cloud panel.
You can literally scale from any plan to max. But according to your present User account type, there can be some limited quotas upto which you can scale. So if you want to scale to the maximum, request us to change your quotas. Read here more.
Please check operating system page.