Nope, you can easily get access to your files via USB. As for storage on iCloud, any keys would need to be recoverable via your Apple ID password which would likely make it the weak point of the scheme.
Any telecommunications device in the US is subject to CALEA so expect backdoors.
Actually from IOS4 and on, you can't get files via USB directly without entering the passcode. The filesystem itself is encrypted (AES256) and unlocked once the passcode is entered on the device.
However I believe without a passcode you can still just use USB to access everything.
Actually CALEA mandates two things: 1. the ability to intercept, 2. that intercepts not be detectable by end users. You can implement the functionality anywhere in your stack that you'd like, including the consumer device.
True, but putting it end the end user equipment is a bad idea (and probably opens you up to liability) because it can be detected and mitigated from that side. You have to assume that whatever code you're running on a device not under your direct control will be observed and poked and prodded.
I'm not familiar with iCloud. Does it have strong client side encryption?