Best workflow practices for iBooks Author re Enhanced Books?

Question

Hi
I have already published one Enhanced iBook in iTunes (The Wandering Gorillas) about my research in Rwanda.  I am now working on several others which will contain much more interactive media - photos and video.
I have vast amounts of unique photos and video - which would be useful for education purposes. So, 'where fools rush in...' I began to creat a new Enhanced iBook with lots of rich media.
However, I immediately started to have serious problems as the fille sizes grew very large - due to the many images and especially because iBooks Author creates versions etc.  Thanks to solutions provided on another post by Pondini & Linc Davis these problems have now been resolved and I have regained my 'lost' 100 GB - which had been gobbled up into the folder DocumentREvisions and private/var - you can read their solutions here
https://discussions.apple.com/message/22800295#22800295
Now, I wish to avoid the same problems - and try to get the best possible workflow to use when creating Enhanced iBooks - which contain lots of rich media files such as photos and video.
And so I am asking advice form anyone who has created such iBooks using iBooks author - or who is an expert in the finer workings of this software.
First -  Since Apple restrict the final iBook size to 2 Gb (and recommen smaller) I am considering creating my new iBook via separetly published chapters - so that each will be less than the max 2GB.  Obvioulsy these will have to have some 'stand alone' usefulness!
But, is this a good practice? has anyone done this? Is there any way for the separate chapters to be later combined - by the user - in order to have a complete, coherent book?
Second, re image file sizes.  For best quality on their new Retina Display iPads Apple suggest images of (No larger than ) 5000 x 5000.  I used this - and it produced image file sizes of 20 -30 MB.  I did some other trials - using images of 1024 x 1024 max - and on my iPad 2 (non Retina) my failing eyes could not see any difference?  Their file size was reduced to 2- 300 KB
Would the difference be  obvious on a Retina Display though?  Should we use the largest possible resolution (and file size) - but this has serious implications for the eventual overall iBook file size.
What is the best compromise?
Third,   I have an iMac with an i7 250 Gb Flash drive and a separate 1TB hard drive.  All my 'media assets' are on the 1TB hard drive. The still images are exported from my various Aperture libraries - as jpegs of the size mentioned above (and into a newly created folder) .  Same with video - to Apple's recommendations for video replay on iPads.
So far I have kept and used the actual iBook Author file - for the new book - on the desktop of my 250GB i7 Flash Drive.
But, as I reported in the other post, this soon caused me huge problems as my disk space was rapidly 'eaten up' by duplicate versions etc.
I am now considering using a separate, 1Tb Firewire External drive for the actual iBook Author file (with backup copies onto another 1TB drive) I am certain this will be slower than using my internal flash drive - but is this 'good practice?'  Can it avoid the problems of all 'lost' storage space which caused me such hassles when using my flash drive?  Or, will this be minimised if I create separate iBooks from separate chapters?
And, delete uneccessary versions of course!
I do feel that this is an emerging issue which many will face - as we incorporate more and more rich media into our iBooks.
Any help or suggestions are gratefull received!

Answer 1

Thunderstorm played havoc with box from my ISP - and I am ruuning on a reserve and internet access flaky!
but, here goes with one reply.  Will have to wait later re tests for your other suggestions when weather calmed down
Re   'as Apple suggessted'   I should have said - no larger than 5000 x 5000 pixels (the 3240 was my vertical proportional dimension from choosing 5000 horizintal dimension)
this is from Ibooks Author help
Add and edit photos and other images
You can add a photo or other image (in a supported file type) to a page in your book by dragging the photo from theMedia Browser, the Finder, or another application.
After adding a photo to your book and positioning it on the page, you can use the tools in iBooks Author to mask (crop) the photo; change its brightness, contrast, and other image qualities; or erase its background.
Important:  When you export your book for distribution outside the iBookstore, images are automatically scaled to a width of 2048 pixels, which is optimized for iPad with Retina display. Readers can view these images on other iPad models, but the viewing experience might be slower. You can improve the viewing experience on iPad models without Retina display by using images no wider than 1024 pixels.
ShowMask (crop) a photo
ShowChange a photo’s brightness, contrast, and other settings
ShowRemove the background or unwanted elements from a photo
Important:  Images can’t be larger than 25 megapixels (5000 x 5000 pixels) or 50 MB.
SEE ALSO
Add an accessibility description to an object 
Add a title, label, or caption to an object
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