Here is a link that has a ton of great idea. You can also search for pedestal sink storage on Amazon. https://www.google.com/search?q=storage+under+a+pedestal+sink&rlz=1C1CHFX_enUS802US802&tbm=isch&tbo=u&source=univ&sa=X&ved=2ahUKEwj00q7Fo6ffAhUmWN8KHbC8AoIQsAR6BAgEEAE&biw=1194&bih=874
I use decorative baskets.
I Use a very small cabinet.
Shelves or other storage above the toilet will help. I've seen pedestal sinks skirted so there is extra storage, but, I thought it took away from the sink's appearance.
My grandmothers sink had a skirt and she only kept cleaning things under it, but you can used the stackable shelves and drawers that will fit under the sink.
I would use a small storage cabinet and cut the hole needed for the sink and let it rest on top. Then caulk and it should work out fine.