You have found the Achilles heel of digital video.
Video takes lots of memory. You just discovered that. When a digital camcorder/camera is capturing video, the light/image passes through the lens, hits the imaging chip/processor and is digitized. Through the various electronics in the camcorder, the video data is compressed, then written to the storage media.
The compression applied extends or reduces the amount of time available to be recorded in the storage space. More compression = more discarded data = smaller file size = reduced video quality.
Less compression = less discarded data = larger file size = improved video quality.
Remember, this is at capture. This sets the stage for video quality downstream. You can always reduce the video quality later, but if the data was discarded or was never there at the beginning then there is nothing to "get back". All this compression/quality nonsense is specific to the storage media - not anything downstream (yet).
Once captured, if all we want to do is playback the video, there are computer-based players (like VLC player from www.videoLAN.org) to deal with the compressed video file. This does not help with your AppleTV environment - but that should be for edited projects, only (in my opinion). If editing is needed, then - usually - the video first needs to be decompressed. This is where the size explosion happens.
In the days of standard definition video, importing 60 minutes of DV format (low compression) video suitable for editing consumed about 13-14 gig of computer hard drive space. High definition video (HDV format) came along - and importing 60 minutes consumes about 44 gig of computer hard drive space. Then came memory cards and a new compression technology, "AVCHD". It was originally designed to store high compression video for consumers back in 2006 as the evolution to flash memory and hard disc drive started. JVC had its line of internal hard drive consumer cams that stored DV/HDV format, but for whatever reason, they were short lived (but I digress).
The "decompress before editing" continues to be a requirement. So, you are right - if you record at the lowest quality setting and decompress for editing, that will take up the same space on the computer's hard disc drive when compared to capturing video at the highest quality setting and decompress for editing. The deal is that the video saves storage space at capture and allowed for more video to be recorded to the storage memory of the camcorder. But that compression at capture comes at a price - discorded video data (and reduced video quality). I don't think there should be an expectation of storing the decompressed video suitable for editing... You *can* store the original video (that the camcorder compressed onto the memory cards). After decompressing and "importing" to the video editor and editing, you have a choice. There is no "single best format" for all playback.
My little world: In iMovie (or Final Cut), when the editing is done, I select "Export using Quicktime conversion"... Format: Quicktime movie, select Options, in Video settings, select Compression type h.264, Compressor quality is High, click OK; then in Video size, select Dimensions 1920 x 1080 and put a checkmark in the "De-interlace Video" box. This will compress the video - but it won't be a lot of compression so the file will be large. To answer your question: Yes, you can compress the video to be stored, but we are not done. I *think* the file just created should be usable by your AppleTV (if not, you may need to check the MP4 options when "Export using Quicktime conversion"). This file can also be uploaded to YouTube, Vimeo or other video sharing sites. It can be large. I just uploaded a three minute:15 second video that was about 1 gig. This same video can be used to make a DVD that is playable by a regular DVD player. Using iDVD, the high definition video will be transcoded and downsampled to standard definition video into VOB files. If I want to have the file available on my iPod Touch or iPhone, I use HandBrake from www.handbrake.fr to compress the file into an MP4 file suitable for that platform (the iPod/iPhone presets are handy; then drag to iTunes video and sync). Many times I "print to tape" and export the finished project from the editor back out to the camcorder. This returns the video project to its highest quality, low compression HDV format for longterm storage - it can always be imported back into the computer. This is not available using consumer flash memory or hard disc drive camcorders.
Copy the original video from the memory cards (not import - just copy the MTS or TOD files) to the "long term storage". These are the original video files and on which everything else prior to this was based. You can get to them later if needed. For future editing access, rather than import from the camcorder, you would use a "transcoder" (converter) to get them out of their MTS/TOD file format (video editors don't deal with directly) and into an appropriate format. I use MPEG Streamclip from www.squared5.com. There are lots of others.
So... when you are done editing and have rendered the large, high quality file, you can delete the imported video project files - you should have the originals in the format that the camcorder captured them and they are in your "backup". They can be accessed for playback only - or transcoded for editing in a future project. You have the edited final for sharing/viewing and used for different playback "audiences" - using other applications to transcode or compress.
In you case, you filled a couple of 32 gig flash memory cards. The MTS/MOD files on those cards are the "archive". Your TimeCapsule needs to store these files "forever". The rendered, high quality, final project can be stored on TimeCapsule "forever" and also in the AppleTV box for playback access. But all the imported decompressed video from the camcorder used in iMovie (or FinalCut) that are using all the space but are no longer needed for a video editing project are no longer needed - IF the MTS/MOD files on the memory cards are stored - at 32 gig per card, you just freed-up a ton of hard drive space.
The camcorder manufacturers have done a poor job of helping normal people understand the entire, comprehensive, process flow. Long term, archival, storage is not at all on their radar an we are left to fend for ourselves. I continue to use digital tape for several reasons. In addition to storing a low compression capture format (HDV) from my high definition camcorders, digital tape has a pretty decent shelf life and is inexpensive storage. I wish I had the resources to get a Networked Attached Storage system (like TimeCapsule). For the moment, I don't re-use any tapes (they are the "archive") and the really important ones are stored off-site. Yes, I have used flash memory camcorders (Canon HF S100) so I have dealt with "which files to I need to keep and where do I keep them?" I have the original MTS (compressed files) and deleted the imported, decompressed files long ago.
Remember - this is all my opinion only. Others might think differently, but I am sharing this from experience. I hope it helps - and I hope it makes sense...
1) I think was addressed above + your second to last paragraph.
2) statement - no question that I see.
3) Stabilize on the video that needs stabilizing. You can decide that after capture/import.
4) statement - no question that I see.
5) Final Cut has more capabilities. I have read that Final Cut Pro X is not as good as the previous version Final Cut. It depends on your needs. I like the flexibility of dealing with multiple video and audio tracks (iMovie does not).
8) Sort of. As I understand it, TimeCapsule has a single drive that backs up the data on a computer. A RAID1 set-up would copy the data to 2 drives.
If one of the RAID1 volumes dies, replace the dead drive with a working one (hot swap) and the RAID1 logic copies the data from the remaining drive to the new one. Your back up is is WAY more than many people do, so congratulations on that. I don't trust the "cloud", so a RAID1 NAS is my next investment consideration.
This leaves the 3rd to last paragraph and last paragraph...