What is an "average size" movie? for HD buffs, this is 4GB-12GB for a 2 hour movie, for others it 700MB for the same flick. Also TV shows are far smaller then movies.
But let's assume you are talking about full movies bought using iTunes. HD is ~4GB and SD is ~1.5GB. So you disk usage for 10 movies is 40G in HD or 15GB in SD. Add ~5GB for photos and apps and your at
45GB for 10 HD movies, 1000 photos and 50 apps - 64GB iPad
20GB for 10 SD movies, 1000 photos and 50 apps - 32GB iPad