1. Do I need another monitor besides the LCD on the camera to check focus etc?
Not 100% necessary, but useful. The more you focus pull the more necessary one will be.
You can view at upto 10x for the initial focus. Eyepiece LCD viewfinders such as Zacuto are available as well
2. Which is the best slider for price for DSLR?
sorry not my area - try Planet5D or similar websites
3. Which is the best way to record audio? Do I record on camera or external recorder and sync using a slate? I have a BeachTek DXA-SLR available for free. Is it any good?
External recorder - you can sync then using a slate or software such as pluraleyze. can't comment on the Beachtek
4. Should I use Magic Lantern software or original Canon RAW? If magic lantern, then which version?
Canopn does not record RAW Video. Regardless of whether you record RAW or not the Magic Lantern is recommended for the 5D3 (not available for the 1DX) for focus peaking etc.
5. What is the ideal ISO for video? And if not ideal, what is the acceptable range for noise free work.
ISO160 or multiples thereof if required
6. Is 1/50 the only shutter speed to work at or it does not matter?
You can set the Framerate in the camera - so depending on your output you would set the shutter speed at double that.
7. Will my Imac be ok for the edit? I will not buy an Imac now until it is refreshed, but just want to prepare myself on the speed of edit.
Can't answer that - but I suspect it would be a little slow for RAW Video editing
Further - one Card ?? You will need several - or a stack of them if recording RAW Video....
ANY help is appreciated sincerely.
Thank you so so much.
This takes me to few other questions:
Which monitor should I buy which can stick on top of camera?
Which version of Magic Lantern? (I believe the latest is in testing)
I do not understand "set the frame rate in camera"
Yes, I need multiple cards. If I was working 12 hour days and recording 5-6 hours of RAW video, how many 32 GB cards does that translate into?