I am also a Rocky Horror fan, I have loved the film for years and have attended the Stage show a couple of times in a full Frank outfit, I had never really thought about editing the film but your ideas have got me thinking, my thoughts:
Edit 1. This should be relatively easy many programs allow you to mirror video, and for audio you could either just use the original mono track (which I believe is on the Region 1 DVD, but annoyingly for me not on the Region 2), or just flip the channels of the 5.1 track, there are a few programs that can seperate out the channels into .wav files then all you'd need to do was re-name the left to right and the right to left and re-combine them. I have no use for this edit but I wish you luck in completing it.
Edit 3. this would deffinitely be more difficult and beyond my abilities, it would be cool if done well but I have no advice.
Edit 2. Now this one really interests me, I'd never read much trivia on how the film was scripted but I have been reading for the last couple of days and have found some iteresting stuff. I was reading the script here and it describes the exact shots that were to be used from the referenced movies, and it wouldn't be too difficult to create these titles if you had all those films on DVD (which saddly I don't). It might be worth contacting the guy who posted the clips on youtube and seeing he has then in higher quality since he has various versions that could be used as they are or combined in different ways to taste.
With regards to the black and white I havn't read anything that says the film would be black and white throughout. The stories are either that it should change to colour during the Time Warp when the doors open, or when Frank's face is first seen.
On the dvd as an easter egg there is a version of the film that changes during the Time warp which has a very good impact, but unfortunately the lips at the begining are also grey which looks stupid.
The script linked above supports that it would go to colour on franks face, I think the thing with the lips supposedly being the only colour throughout the film comes from a misenterpretation of the script:
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GO TO COLOUR AT BEGINNING OF FOLLOWING SCENE
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54 INT. LIFT/HALL NIGHT
The figure turns and throws open lift cage door. As camera zooms in to
the death mask above them the film changes from black and white to
colour. However the only colour in evidence is the red lipstick on the
mouth of their host.
I think rather than refering to any post preduction trickery this just refers to Franks face being white and grey except the lips so they stand out, the next shot would then reveal everything in colour.
Personally I wouldn't want the Time Warp to be black and white even though that's how it's scripted, I like the transition on the DVD easter egg it works really well with th look of shock on brad and Janet's faces as they enter the ball room, but it doesn't work with the titles.
But also from the script there is more on this in the script amendments at the end:
1/2 The film will now commence in Black and White on "ACADEMY"
format. It will extend to wide screen (1.1 - 85) at
Sequence 41, while still remaining in black and white. At
Sequence 54 the film changes to colour.
so this means the plan at one time was to start with 4:3 ratio Black and White up until the doors open during the time warp when it would change to widescreen (1:1.85) but still black and white, then change to colour on Frank's face (and during that shot his lips would be the only colour due to the make up).
I'd be curious to see it edited closed to the script and I might do a version of it myself, although I'd want to use the original mono track to give it a more authentic sound and I don't have a copy, I won't be starting this anytime soon (although I might play around doing some rough cuts), but I'm happy to discuss ideas.