I do that with my Medion tablet, it has 32gb of memory and also takes a 32gb micro sd, it's an excellent bit of kit about the same size as the ipad and runs android.
Got mine at Aldi so has a 3 year warranty, think it was £140 with a free micro sd.
I've just bought a 9.7" galaxy tab A, and so far am very impressed with it, it will take a 128GB micro sd card for all your films and music, no need to mess with usb sticks,
About 8"-10" mainly as its primary use will be for viewing. I have a iPad for work but it's no good for anything I have downloaded on my android TV box.
USB or Micro SD would be fine, I have a few big storage USB already so it wouldn't bother me if I did watch most of the content via a stick.
I had a quick look in Currys/PC World today and they seemed to have a fair few for £150ish only a couple for £200-£250 then they seemed to jump to about £320
I think I would only consider buying one if it had a sd card slot, by their very nature of being portable and used in various locations I don't like the idea of a usb sticking out waiting to be snapped off if dropped or similar.
I bought a bush 8" for about £70
I watch movies and browse iternet on it.
Got a 64gigglebit sd card from currys for £15 that holds about 4000 books, couple of hundred hours of music, and about 10 movies
Battery life is quite good as well - 8-10hrs of playing video/reading on a full charge.
Triple that playing music with screen off