Apart from the actual set up to include org-capture in it, not much.

Shortcuts to open a file (C-x C-f), close it (C-x k), and closing emacs (C-x C-c) would be the emacs shortcuts you'd need to learn. The rest would be org-mode shortcuts, like setting something as done (C-c C-t d) etc.

You will have to get used to being in Emacs though, that's for sure :)

Take a look at Checkvist. No emacs knowledge necessary, just heirarchal notes where you can set due dates and whatnot.

Not much. I hardly know emacs (would love to learn more though...) and am using sublime as my editor, but have learnt just a few shortcuts to be productive in orgmode. Currently I run emacs just for my orgmode tasks and org-agenda which is fantastic.

Maybe the Spacemacs distribution of emacs is more accessible for emacs beginners. But beware: it is really opinionated.