I installed ML on my 50D but I don't see RAW video anywhere? Do I need to get the latest nightly or?
You need to load either the
mlv_rec or
raw_rec module, and then enable one (not both) under the Movie tab.
Any ideas if the RAW feature for 50D will go to stable release any time soon? How stable are the nightly's? I don't mind if camera crash from time to time but I'd hate to brick it (it's the only decent camera I have)
There currently isn't a timeline for the next stable release. The nightly builds are pretty stable, but there will occasionally be broken builds (hopefully fixed soon after). I don't believe there's been an actual instance of ML bricking a camera in a permanent sense, but rarely a camera may end up in an odd state and need to be coaxed back to normal, which could mean days/weeks of downtime.
I remember in the 50D manual there was talk about "you cannot leave LV on for long because sensor will overheat" - I see temp during RAW recording (nightly) goes to 50C fast how safe is that?
I don't know if it's possible to quantify the safety. At the warmer temperatures, you may see some variation or artifacts in the sensor output, and the 50D has a quirk where the FPS may lock to 22 fps.
what is the difference between modules that record MLC and RAW wrt 50D, I see that MLC adds some meta data and RAW is just raw but anything related to 50D I should know of? some use more ram then the other? some need more io then th eother?
Since the 50D can't do audio, the primary benefit of MLV is the useful metadata. I recommend using MLV unless you find that it's not performing well enough for your needs. If that's the case, then see if RAW makes a difference.
and final question, can't find the "crop" option anywhere 
Press the 5x zoom button in LV mode.