Since you only get one question, I'll choose the second one as being more helpful. I have included an enotes link to a biography of Cezanne so you can read that for yourself.
The bigger issue is how much richer the poem will be for you when you have done a little homework on the artist and his works. The poem is the narrator's advice to a friend who paints; he suggests he take a look at Cezanne's work. Specifically, he refers to how the artist shows his "lay of the land," how he paints "the bather in his sketchy suit," and his blushing apples," among other things. Those are specific references to Cezanne works.
A quick image search for Cezanne's paintings of apples, for instance, shows several dozen different paintings (which I've also included below and which happens to have the bather painting, as well). By looking at them, one can start to develop a sense of his style and how, exactly, his apples "blush." The same is true for every image in the poem. The advice only applies if you understand the reference point.
Let's be honest. The artist friend referred to in the poem's title is probably quite familiar with this famous artist's works. Not everyone is. If the reader has no clue about Cezanne or his works, this is a fairly meaningless poem. The meaning is tied inextricably to the artist and his art. The good news is the allusions to Cezanne's paintings are quite knowable with a little effort. Then, the richness of the images is accessible to the reader, not just the "friend."