Yes, the poll is a bit ... wide in scope to be politically correct.
Now, I'm not sure if you're an actual software developer or a internet property developer so I'll try to cover both
If you plan on developing this yourself I suggest you use the technologies you know best if they are aplicable to the project scope. I doubt Mathlab or Flex would be good ideas though. Depending on your skillset you might want to find at least another person to join the team, a project of this size and potential risk should not be taken lightly.
If you're in it to develop the business then things are different. The first step would be to figure out a realistic budget alocation for the design and development part of the business.
Depending on the figure you come up with you will have have access to different technologies and talent for your team. I suppose it will become a choice between releasing something cool fast and then update if it takes off or building it heavy duty from the ground up. I don't know what your exact plans are but I generally advise a release early, update often approach. This way you can test the concept fast and make use of invaluable customer feedback rather than risking to blow your budget too soon on non-essential stuff.
Now, your question was about the development technology and I went a bit off-path. I think you should go with the classical php back-end with a smartly designed responsive front-end with well optimised ajax integration (includes JS, obviously). You could also try Ruby, bit hipster but quite cool and effective.
You shouldn't need much more than that to get you started and in the mean time if all goes according to plan you can invest in optimizing the most crucial parts of the business or doing a whole new back end if you feel you need to scale it to enterprise levels. Once you get there I'm sure you'll find a suitable technology, like Java with it's many enterprise level frameworks. However, the deeper you go into big business territory, the more expensive the technologies and the talent.
Hope this helps.
Cheers!
PS : Don't skimp on the user interface and experience
PS2 : Don't group Java and JS together
Thank you for your really really helpful insight.
off course I will not be in this alone, I hardly specialize in 2 of the mentioned languages, I m planning to launch an Elance project to hire the most efficient team to get things started, hence the whole scripting language question.
I totally agree with your release early and update frequently approach and is something what I am aiming for, but lets face it none of the exchanges out there right now are anything but perfect, so I was hoping to learn from their mistakes.
Like someone said developing something in Matlab would be the most secure thing ever, whilst personally I dont have the level of skillset required in Matlab to pull this off hence I will hire someone.
But what about the desktop application ? will php/ajax/ruby successfully and securely integrate with the desktop application ?