Re: the OP, that's a bit overkill.
* The usbnet hack already properly supports sshd @boot without having to write an init script [BTW, the one linked by the OP will only work on devices using sysvinit, not those using upstart (k5/pw)], check the config file/the docs.
* The usbnet hack also properly supports sshd over WiFi, without having to play with the firewall, again, check the config file.
* I'd recommend simply authenticating via shared keys instead of playing around with passwords, but that's left to the reader's choice
.
* And, err, that's all, anything that can speak SSH/SCP/SFTP will work. On Android, like Mike L said, I'm a big fan of ES Explorer.
Again, most of this is explained one way or the other in the USBNet doc. (Hint: if you want a seamless setup, sshfs?).
And, yep, on the 'vanilla' side, anything over HTTP should work (a simple webserver, like in the post linked above, or a nice OPDS thingy, like the Calibre content server, or any of the others [some of those are developed by MR users, check the Calibre forums]).