A. A. The DMW sets up an "aggressive" set of dbcc and other healthchecks. On "large" databases this sort of housekeeping can take a long time, so you might not want to do everything every night. In this situation you might want to set up your own maintenance tasks, perhaps only running checkdb once per week, and newalloc every night, with index rebuilds once a month or so.
MS's choice of "large" is 400Mb - probably a bit low given the speed of current cpu's/disks etc. The answer is, if you're happy with the time it takes to run the DMW generated tasks, then stick with it, regardless of your database size.