NetworkGuy - no offence taken at all, I totally appreciate that I come across as a total idiot - and as far as technology goes these days, I am. Hard to believe I used to teach the stuff isn't it
However, I assure you that there aren't any actual 'duplicates' There are quite a few 'sets' taken on auto, so 20 in a row of a child on a swing for example, but no actual duplicates.
TotallyBSYou know how kids these days are attached at the hip to their phones - well, I have my camera
So, 10,000 does not surprise me in the slightest, otoh, they are high resolution, so might be a few less 
I don't think I realised how 'small' my HD was actually, so really, I shouldn't be surprised at the 'fullness of it'.
I think, for now, I will try to delete everything off of the TB, re-save it, re-do the backup etc and buy another smaller HD for the second back up of photos and possibly another to keep at home
Then be very brave and delete them off of the c-drive.
Maggie - you are more than welcome, carry on! :)
TotallyBS & others - I tried to run the ccleaner this afternoon, but it got 'stuck' at 2% and didn't get past it for several hours?! I'll try again tomorrow.