Stéphane,
looking at your library I see, that the structure is already very sound.
You are having projects names by locations and dates, contained in folders grouping them by locations - Paris, Germany, America, etc.
See the projects and folders as storage structure, like Kirby's User Tip explains.
The albums you create will give you a more convenient retrieval structure, and that should reflect, how you most frequently will want to access your images.
If family photos are important to you, create albums and folders with family members and family events; if you are into wildlife and nature photography, create albums with wildlife and nature selections.
Most of my albums are smart albums based on keywords and other tags. I use hierarchical keywords:
Nature > Animal > Predator > Lion
Cheetah
Leopard
Nature > Animal > Bird > Condor
> Vulture
And based on these keywords I have a folders with several smart albums like "Keyword is Lion" and "Rating is > ***"
Another folder contains scenery albums, and another one albums for flowers and and other plants.
Keywords are very convenient to assign an image to several albums at once.
Léonie