I'm not clear on what the minimum vote threshold is to greenlight a job?
I have not looked closely at the final code yet but I believe from earlier discussions there is a "return" item which sets the line for approval. Anything below that line will not get funding because it will instead go to the return item (returned to funds).
Will it be up to the individuals proposing the work to essential market it?
It may well be. What is not clear is how this will work out in practice (by which I mean community expectations and voting, typical sizes and granularity of proposals, etc.). As far as notifications and such, I do not believe there will be any in the basic steemit.com UI, but there are many other dapps and services available which make take that on.