Thing thing with lens focal length is there are no good and bad, no right or wrong. An example of this: Martin Scorsese hates long focal lengths and uses wides, where as Akiria Kurosawa used long focal lengths extensivley, filming entire films on them.It depends on you and your projects and your personal style.
That said, many famous filmmakers are advocates of 'learning' on a 50mm focal length, which would be a 32.25mm lens, or 30mm to make it even, it's a normal perspective so you can't really go wrong.
It's a very personal affair, the lens (camera) is a tool and I can guarantee is Refn, Haneke, Boyle or De Heer shot their next feature on an iPhone I would love it.
That said, I was unsure of what focal lengths to use to, I didn't want the Kit Lens (Great choice as kit lens is shitty IMO) I wanted to start getting primes and I started out with the 50mm 1.8 like you (which is a 35mm 80mm on your camera, great short telephoto length for portraits/medium close ups and talkies etc) so I got a cheap zoom that covered the 'normal' range so I could test each focal length and see what my next prime would be. The cheap zoom I got was the tamron 17 -50mm f2.8 constant aperture (around 300 delivered from DWI, Grey Import)
I have a Canon 600D, same crop as yours so it's effective field of view is around 27mm - 80mm on it. It's a really good lense and stays on my camera 95% of the time, if you've got enough light and dont need that extra couple of stops (going down to primes f1.4 etc) then the Tamron is an excellent choice to begin with.
Because of the time spent with this Zoom lens I have narrowed my first prime down to either a 24mm, a 28mm or a 30mm (38mm, 45mm and 50mm respectively). I'm leaning more towards the 30mm as Sigma make a pretty good one that isn't too expensive, the 30mm f1.4 which shouldn't be too much more than $400, if you're in doubt go 50mm right?
If I had "a lot of money" (what does that mean anyway? Can you post your budget so we can get a better idea) I would get a better camera, but that's just me.
For my 600D if I had a decent amount of money to spend on lenses I would get:
Canon 50mm 1.4
Sigma 30mm 1.4
Tokina 11 - 16mm 2.8
A 24mm, probably the Samyang or something in that price range
Don't forget about Audio, it's (more than) half the viewing experience and people will forgive flaws in PQ easilier over flaws in Audio!