I think the 570 with the AMD Athlon II x2 x 250 processor would do you just fine. (stay away from the Sempron processor)
The 4 gig of ram would be enough unless you start doing photo editing and batch processing.
I just setup a similar Dell computer for a relative who does pretty much what you will be doing.
He really likes it and is a huge improvement over his previous 9 year old Dell.
He streams movies without a flicker.