I would like to have a good intuition on how close is what animal to which one and how large each group is by number of species and population. I was wondering if there is a good website with good demographics and graphs that could help me memorize it because it's really so hard to make up the tree myself from wikipedia pages!
There is a very good website and application for that. It's called Onezoom tree of life explorer which I believe is for London imperial collage.
Another alternative is the Tree of Life web project, which includes species richness information in the lower levels of the tree and allows reasonably easy navigation of subtrees. You can find the animal portal here.
EDIT -- another alternative, which is in active development, is this integration of Wikipedia and the Open Tree of Life Hyperbolic Tree.