1. Nope, that's only needed for the jailbreak. No need to uninstall anything else (found here, at least) to update them
. (So that answers your question: uninstall jb -> install jb -> update (install) usbnet)
2. Uninstall every hack (jb last, you got that right before), then do a factory reset. Or flash a full image (cf. the debricking guides).