It seems that an USB cable is still required.
The article in Apple Support that shows how to import videos into iPhoto has not been updated recently. Either Apple is still behind in updating these support articles (not likely) or there is nothing to update--in other words, you still need USB.
The release notes for iPhoto 9.2 list the major updates to the app. It mentions that iCloud support is now included, but nothing specific about importing videos wirelessly. Hope this helps.
Photostream will store the previous 30 days worth of photos automatically. That means, every photo you take on your iOS devices will be sent to Photostream, but only the last 30 days worth of photos will be available there.
If you enable 'Automatic Import' of Photostream in iPhoto (Preferences > Photostream > Automatic Import) then when you launch iPhoto, it will automatically download a copy of any photos that are in your Photostream, and automatically create an Event titled: {MMM YYYY} Photo Stream (eg. "Jul 2012 Photo Stream")
This Event will be automatically kept up to date, as long as iPhoto is open long enough to sync everything required (depends on your connection).
In effect, as long as you open iPhoto once every 30 days and leave it open long enough for your Photostream to be imported, you should never have to manually import a photo from your iOS device at all.
As for removing items from your Camera Roll on your iOS device, as long as you see that they are present in Photostream (or in iPhoto), then it is safe to delete them from your device. (There is no way around this but to do it manually as far as I know.)
Currently, Photostream does not support videos. To import videos, connect your iOS device to iPhoto and import these manually.
As a side note, in order to keep some photos on the device, you can create a smart album in iPhoto along the lines of "Photos taken within the last 30 days" or "Photos rated 4 stars or more", and configure iTunes to sync these to your device. That way, you can be sure that no matter if you clear your Camera Roll on your device, or delete certain photos, you maintain some convenience.
Best Answer
Apple wants you to use their PhotoStream or do manual syncing all the time. From my personal experience it's impossible to manage some parts in PhotoStream and some others outside. I'm sure it's possible to do some crazy scripting, symlinking and syncing. But hey... that's not the reason why we use Apple products in favor to the more open Android ones, right?
I ended up re-creating my Aperture and iPhoto libraries and a big upload session to PhotoStream. Works fine so far.