Yet I have 5 Opera processes (plus the crash reporter)
This is normal for all Chromium based browsers as they work in a multi-process scheme. As said, you have one process for the browser itself, one for each (individually) opened tab, one for each extension and so on.
and of the top 10 memory consumers they are 1, 2, 4, 5, and 7.
If you enmable the PID column in Windows's task manager, you can use Opera's task manager to see what are those processes.