Global tuning
You case select all tones by Ctrl+A. There are also some other selections in the Edit "Select special" menu.
In the Edit menu there is Quantization Macros / Correct Pitch dialog. You can use that for auto-correction of the selection.
Algorithms
In the Algorithm menu you can set required algorithms as well as default one. Every time you change, current file will be re-analyzed.
Polyphonic algorithms are available in Editor and Studio only. Note that you want that algorithms for everything except natural monophonic. So dry voice, flute, etc will work fine with Melodic. But piano produce overlapped tones even when you play a melody. Keep that in mind when considering Melodyne version. For general purpose I recommend Editor. I do not support most features of Studio and Essential has only basic pitch operations.
Preferences
I recommend to disable automatic check for updates. I am not sure that Sibiac will work without changes with the next update.
Other important settings are in Audio and Default tuning in the User interface.
Warning: be careful with shortcuts page. If you are in shortcut page, navigate to the page selector and change the page. Even in case you just want close preferences. In case some action is currently in learning state, any key or combination, including Escape and Alf+F4 will be assigned to this action! There is no way to tell Melodyne to stop learning, except by changing the page. Note that even in case preferences dialog is closed, when you open it again Melodyne will remember that you are learning action.
To assign a shortcut, in the shortcuts tree select required action with up and down arrows. Sections can be opened and closed by Enter.
Once required action is found, press Enter. From that moment any key you press on keyboard is assigned to this action. Even in case you tab out of the tree. Till you switch from the shortcut preferences page. You can delete current assignment by first entering learning mode for the action in question, tab to delete button and pressing enter.