Yes Android has much more flexibility to do what you want on the device. It's easy to mange files on stock Andriod. I believe you can do the same on iOS but that requires you to jailbreak your device.
I don't know the price of the Xoom, but that is a device I have my eye on. It will run the latest version of the OS with a dual core processor.
If your father is downloading his books from manynet, they also provided "Mobi" format which is native to the Kindle. You do not have to convert anything. Tell your dad to point to http://mnybks.net/
(that is the mobile version of manybooks.net on his kindle and he can download the books directly from the internet to his K3.