@starlord
The head artist should be in charge of the art and establish the style and coloring technique for the site, with the owner's discretion of course. They'll be making sure that all art assignments are given out accordingly with a set deadline in order to meet the monthly pets/items/etc. Keeping a backup of all of the art asset for the pet site as well will be a duty that they'll carry out. Having an account on an image hosting site for example, and putting them in separate folders/categories; organizing all of the art presented on the site. I also think it would be vital for the head artist to help host official site art contests/ user-made pets/items to be used on the pet site for another example. (also there only needs to be 1 head artist and 1 head mod in the beginning...maybe a max of 2 of each unless you know you're going to have TONS of members and the head artist/mod need the help)
These are just my thoughts and not necessarily what starlord will be giving all of these tasks to the head artist. Especially since starlord has already been planning this site before.
Also here's another thingy that I posted in another thread to help!
Disclaimer: You've already started on your project, and in no way telling you you have to do it in a certain way. I'm only making a suggestion + giving a tip.
Just going to pop in and say that you guys should probably make a to-do list and tackle things one at a time.
So first decide what the site will offer players, what will it be like, what features/mechanics will be implemented, etc.
Then look into what you'll need in terms of art. Species, items, NPC's, logo, etc.
You could probably google for a guide on where you should start. It's best to not dive right into making the website/app until you have everything else (concepts you decided on, art, finding programmer/web dev, etc.) completed. That way you won't be paying for a domain for so long and waste that extra cash for example.
Also, you don't need an overwhelming amount of staff members either. Using CS as an example, there are TONS more users than staff members. Working with a small dedicated team will be much easier when it comes down to forming meetings and being able to communicate without having a ton of staff members that are all contributing at the same time which can be a lot to take in.
From what I've seen/heard creating an adopt/virtual pet site could take a year or even a couple of years depending on the amount of work it will require as well as the resources you'll need and how long it will take to find the staff you need (since sometimes a staff member may disappear or can't volunteer anymore).
Just wanted to throw in my own two cents and help you guys out a little.