Hi mitchstein, just jumping in here with answers/solutions to a few of the remaining open questions in this thread:
1) 15 categories, 40 shows per category 600 unique videos maximum per channel.
—> The limit content limit for Direct Publisher channels is actually 25 rows, 40 content items per row. This comes out to 1,000 unique content items per channel. This can be a little deceiving, though, as series and/or seasons both count as only one content item.
In your case, you'll want to list each season as its own object, and list seasons and episodes as its children. Using this schema, you can include the complete catalogue for 1,000 seasons in a single channel. All of this content will be available in Roku Search (from the home screen) and from the in-channel search feature. Note, though, that the series and season mediaTypes are only supported in JSON feeds: https://github.com/rokudev/feed-specifications/blob/master/direct-publisher-feed-specification.md
2) Channels update in accordance with our feed downloader, which re-downloads the content feed every 4-6 hours. You do not need to resubmit or update your channel. This may beg the question of "what happens if I want a piece of content to go live/be removed at a specific time, and can't rely on the downloader's schedule?" In this case, you'd want to use the validityPeriodStart/validityPeriodEnd fields. Again, these fields are only available for JSON feeds.