You're welcome. I think that Android would be the safest and best choice for those kind of tasks. Mainly because of huge number of applications to choose from, which could help you to manage all of your work. Another thing is that Android is much better when it comes to multitasking and it looks like you'll be using it a lot.
There's a lot of good and powerful still smartphones which suffer because of lack of new Android versions. This is where developers scene comes in, providing you with all sort of goodies, including newest versions of the system. So picking a popular smartphone is key to gain a support for years, even after the official one will not be available. The great example of this is Samsung Galaxy S. It's 3 years old, left with Gingerbread, many would say it's also weak considering the new hardware available in smartphones but it has enourmous amount of roms and developers working on it. You can install stable 4.2 or 4.1 already, the question is if this is what interests you. When it comes to hardware, it depends what kind of hardware we're talking about, the strongest single core smartphones like Samsung Galaxy S, Samsung Galaxy S+ or Desire HD are powerful enough to handle Jelly Bean fairly well. Talking is one thing and seeing is another, here's example how does 4.1 runs on old device like SGS:
http/www.youtube.com/watch?v=7fkn2AfkWIg
It's smooth, definitely usable and suitable for daily usage. As you can propably imagine, it does works much smoother and faster on more powerful dual and quad core smartphones like SGS2, SGS3, Note, Nexus 4, HTC One X and others. The questions is, would you prefer to have official support for as long as possible or you're fine with not official one as well. The best way would be to get a mid, high end smartphone which is very popular. You have to take in mind that official support costs, it costs a lot.
The only concerns regarding your usage will be battery life and of course enough power to handle all those taks without problems. Tell me how much you're willing to spend and we can think of good smartphone for you.