HBase schema/key for real-time analytics solution

You've got the gist of it, yes. Both of your example queries filter by date, and that's a natural "primary" dimension in this domain (event reporting).

A common note you'll get about starting your keys with a date is that it will cause "hot spotting" problems; the essence of that problem is, date ranges that are contiguous in time will also be contiguous servers, and so if you're always inserting and querying data that happened "now" (or "recently"), one server will get all the load while the others sit idle. This doesn't sound like it'd be a huge concern on insert, since you'll be batch loading exclusively, but it might be a problem on read; if all of your queries go to one of your 20 servers, you'll effectively be at 5% capacity.

OpenTSDB gets around this by prepending a 3-byte "metric id" before the date, and that works well to spray updates across the whole cluster. If you have something that's similar, and you know you always (or usually) include a filter for it in most queries, you could use that. Or you could prepend a hash of some higher order part of the date (like "month") and then at least your reads would be a little more spread out.