1 - That's up to you, but I've done several projects for clients with ML RAW in the last year and it did not fail me once. A little bug here and there, so of course do your testing and take precautions (more than one take of anything, check with MLV_Play whenever possible)
2 - With a good card. 24p is relatively easy, stable 25 at 1080p might be a little harder to get.
3 - I've battle tested two Transcend 64gb 1000x: one year, countless writes-reads, never a problem. There has been Komputerbay users with and without problems, but my money is on Transcend. Lexar also has a good track record but I've never used their 1000x cards.
4 - Or would you rather pick the Canon C100 if constant and reliable video camera is needed?
Yes and no. If you want/need/fancy RAW, 5D3 (and if you ask me with 1.1.3 firmware) is the way to go. But, if you are doing client work with little or basic color correction and you cannot afford any tiny glitch whatsoever, I would suggest not using edge bleeding code, even if it is more stable that some manufacturers' factory software. Take into consideration also the different requirements of hard drive space between RAW and AVC/ProRes (C100).
RAW in 5D3 is relatively bug free in my experience and has many advantages, but it all depends on your risk assessment criteria and how comfortable you feel using one solution or another. They are tools, they all can fail, and I wouldn't really compare one with the other.