Hulu has decided to make its platform one that is incompatible with several devices. Standard hulu is supposed to only be available through a PC, Mac, or, I imagine, a Linux computer. As far as hulu plus compatibility, I believe they're rolling out support for various things, but I haven't kept on top of that.
When it comes to listening to MP3s, it's pretty clear you're looking for a cell phone, tablet, or netbook, rather than an e-reader, since I don't believe (but have no real idea) that eReaders can play music.
That takes you down to this list:
Netbook
iPad
Android Tablet
Smarter Smart Phone
NGP (Depending on if it supports the Android platform or not)
The net book isn't a phone, but it would perform word-processing abilities best. An attachable keyboard would make the iPad suffice as a decent word processor. The best gaming device is up to a matter of opinion. The NGP could be the best choice if it can play Android software, as you'd have access to all the games in the Android store. An Android device could be portable and play various system emulators. The iPad is the current App-gaming king, due to sheer number of titles.
Technically, a netbook with a 3G or 4G media card or USB dongle would be your best bet. It could make phone calls through something like gmail or skype, it would definitely play MP3s and hulu, it would have the best keyboard for writing, and it would only lack in regards to gaming, but even then flash games, emulators, and low-end PC games could be used.
Next, if you really want to do word processing, but don't want netbook, comes the iPad, followed by an Android tablet. I like the versatility of the open Android market, but there's no denying that the app store for iOS devices has tons more available, though I'm sure you could connect a bluetooth keyboard to an Android tablet.
How much are you interested in spending? If you set a total budget, you might be able to find a pretty nice combination of things on the cheap when it comes time to put down your money. For instance, Motorola's current top tier Android phone was on sale for a penny from Amazon with the full contract with Verizon just a few months after its release. Other Android devices could always see the same markdown, allowing you to spend your money elsewhere, on a 3DS or something else.