Hey Dan!! I saw you on the train this morning. This is Matt – from the lab back in the day. Reprezent.
I’ve only worked with HD a little, but I’ll tell ya what I know. I don’t think AE really concerns itself with DPI (someone correct me if I’m wrong), it just looks at the height and width in pixels. Just make sure you’re artwork is as large or larger than whatever HD framesize you’re working with and you should be fine.
As far as 8/16 bit – it’ll work with 8bits per channel. If you get any banding, due to the use of a gradient and other subtle color shifts, you can always switch over to 16 if you’re effects support it. It’s good to preview the stuff on a good HD monitor before shipping it out.
Bye Dan!!!!