I use light weight aluminum pans, covered with the non-stick aluminum foil. Never had an issue with those pans.
I have not tried a heavier steel pan, don't know if it'll cause problems, but I seriously doubt it'll do anything better than an aluminum pan except take longer to heat up and cool off.
On the timer - yes you want 10 minutes once the bullets are up to 400*. To achieve that, I just set my timer to 20 minutes and start it when I put the bullets in. I know the oven setting needed to achieve 400, so I set it there at the start and leave it alone.
One further comment on bullet quantity for coating - I realize you were just trying out a handful of bullets at first. However, I've found it's harder to get powder to stick to just a few bullets, compared to a larger batch of several hundred. I typically do 300-400 9mm bullets per batch, which fills a 32oz yogurt container 1/2-2/3 full. I coated 750 of them the other night; split into two batches worked out perfectly. I do go with a fairly light coat so the cake of bullets breaks apart easier (I just dump them all in the pan, no individual handling needed), and try to use the right amount of powder so none is left in the container after shaking them.
