Visipics (free, Windows) -
VisiPics - will sort out your image dupes for you. It works (I presume) by hashing and you can set the sensitivity of the comparison. Many other adjustable parameters in Autoselect mode. Excellent utility.
For combining many disparate folders with sub-folders and sub-sub-folders efficiently you can do it manually, write a script (debug debug debug) or turn to a Mac utility called the Big Mean Folder Machine (not free, but worth it). Temporarily fully Share "My Pictures" on your Windows machine on your network and point BMFM on the Mac at the folders you want to combine. RTFM. UNTICK all the "Subfolders" boxes on the Select Source Folders page (unintuitive behaviour) and make sure you do a Copy rather than a Move in case of accidents (you can always remove the original master folders manually later). BMFM will combine all the original multilevel folders into one big multilevel folder, taking care of any name or folder conflicts that it finds. There'll be a bit of tidying up to do afterwards in the final master folder [Aircraft 1, Aircraft 2, Aircraft 3 etc.) but nothing too onerous.
You may want to run Visipics again on your final master folder cause sure as hell some dupes will have crept in.
Sharp knives, don't cut fingers. RTFM. Sure beats doing it by hand.
Mac
Don't forget to re-restrict your Shares afterwards....
[BMFM is a great tool that can perform many other neat tricks - there are many ways of doing this in Windows (apps, scripting) but none as neat and easy as BMFM]