The Six Odes

Good evening all,

I have recently chosen to do a research paper on Keats and his Six Odes of 1819 in particular. (These are: "Ode on a Grecian Urn", "Ode on Indolence", "Ode on Melancholy", "Ode to a Nightingale", "Ode to Psyche", and "To Autumn".)

Now I know they are considered among his greatest work, but the majority of research I came across deals with the longer poems or one Ode only.

My question to you is twofold.
a) Does anyone know particularly good sources of literary criticism that deal with the Odes, be it one, two or all of them?

b) What is your personal opinion on the Odes as a collection?
- Is there additional value or meaning to be deducted from the clotting together?
- Is it only a matter a convenience because they are written in the same year?
- Is the chronology to be taken into account when they are written in such short time span?
- Which ones do you like better/worse than others?
Anything you have to say about the "lot" of Odes, really.

I'm hoping to learn something from your responses that isn't immediately found in sources, but also to find the essential reference works regarding the odes without having to spend days sifting through the less useful ones.

Thank you, the floor is now yours.