It depends on your current programming experience (if any). It is definitely possible to learn OpenGL ES in a matter of weeks depending on how well you pick up on it. As for real time data for a mobile device, you may want to see how much data you burn through because a constant stream of data to a phone could eat up the users data plan fairly quickly. It might work best if you have it set to update every X minutes as opposed to constantly. However, that all depends on what you are making.
Most android phones should be able to handle what you are wanting to do with not much problem(unless you plan to use a ton of heavy 3d work or something)
If it is charts and graphs that you are making, it might almost work better (depending on your situation) to do this on a website using PHP or .Net and just have the user go their on their browser. That way, the server is handling most of the processing and the phone just gets the end result. That would reduce the amount of data being sent to the phone and also reduce the requirements of the phone.