Easiest solution: Turn off Preferences / File Displays / Mouse / Allow drag and drop into sub-folders (without a qualifier key held down) so you can't accidentally drag & drop at all, without explicitly holding down Shift (to move) or Ctrl (to copy) or Alt (to create shortcuts).
If you really want a confirmation instead, there are a few threads about setting that up on the forum. Here's the first I found, which looks like it's still correct:
(Opus 12.24 is out now by the way.)
See Creating your own buttons in the manual.
Or How to use buttons and scripts from this forum here at the forum.
If you haven't found the manual, you can push F1 to open it from almost any window in the program. It's also linked at the top right of the forum, where there are some other helpful links as well.
Similar to most web browsers, Ctrl + Mouse Wheel or Ctrl + = and - to increase and decrease the font or thumbnail sizes (depending on the mode).
Default font and thumbnail sizes can be set in Preferences, at least in general. If you have trouble setting the size of something particular, please start a new thread for it.
In general, please only ask one question per thread (unless the things are very closely related):