Yes it's feasible to teach 350 students K-8. Many of us do it.
Art teachers can to anything. See if they will give you a room and try
to get at least an hour per week per class.
Make sure your lessons are sequential (though it is sometimes hard to do
this as a first year teacher with so many levels)
Your principal will understand and appreciate the sequential aspect
instead of just seasonal art. Display a lot. Walk through other
schools in your area or go see school art shows and take a notebook.
Steal ideas and develop them for your levels and curriculum. DBAE is
always impressive. (i.e., teach about Monet and do waterlillies with
crayons and wet on wet watercolor wash for water)
Good luck. Impress them like hell.