I'd say medium-medium high heat - I find that the oil can start to smoke at high heat, and it might not be good for the pan.
Make sure to scrub-a-dub-dub the pan first (use a scouring pad, and just water, no soap). Instructions on seasoning here: http://whatscookingamerica.net/Information/CastIronPans.htm
Will definitely need to apply a little bit of oil before cooking for the first few months - but just a little! I pour a tiny bit on and then just spread it with a paper towel.
I'm not an expert but that's my experience.
It says it's pre-seasoned so maybe I don't have to. Also, it says oven safe up to 400 now that I look at it. Only 400?
