All good questions. I can answer some now and will post answers to the others when I confirm.
() As far as viruses/malware/etc. is concerned, one should distinguish between attacks meant to harm your device and those designed to harvest personal information about you. Though there is much discussion of Android devices being the target of new attacks as the use of the OS increases, I'm rather skeptical. (Much of the information comes from those who sell software designed to "protect" systems from such viruses.) If you use the device as it was meant to be used, i.e. not rooted and not hosting software from unknown sources, I don't think there's much to be worried about. What you do have to worry about is providing personal information for "contests" and how the email addresses your wife submits might be used. But in that, even the iPad is a potentially vulnerable device. (It's worth noting in this context that I'm amazed how concerned people are about supplying information like a credit card number over the internet yet will go to a restaurant and hand their card to a waiter/waitress and never think twice.)
() The Kindle Fire does not include a usb to mini-usb cable in the package. I haven't gotten around to digging up such a cable in my house to test it yet but I'll be doing that in the next few days. Once I do, I think I'll find what I know to be the case for other Android devices, i.e. you can transfer images to the data storage (recognizing that we're not talking about a huge amount of stuff. I don't expect to find that an un-rooted KF can host external storage as if it were part of the Android OS.
() As far as browsing/blogging/entering contests is concerned, keep in mind several points. The screen small. Not as small as a cell phone, but small. Accessing desktop websites is possible but there will be much more "scoping around" than on a larger display. Blogging and entering contests will call for entering data. I don't do much of that even on the iPad. I prefer the dual 23 inch monitors sitting in front of me now. And when I do use the iPad for that, I have to use my bluetooth keyboard about 99% of the time. I hate onscreen keyboards. But if your wife isn't as picky as I am and can deal with the small form factor, she'll be fine.