The whole half back conundrum will be interesting but I think they'll probably name Austin at 13 a fair amount and basically give him a roaming role and just let him run/do what he does best. It's a crude comparison but similar to what they've asked L Briscoe to do a couple of times- go out play in the middle and make a nuisance of yourself and make your tackles.
That said, I can't think of any game this year we've had our first choice 1,6,7 available for whatever reason so chances are he'll end up playing half more than he does anywhere else.
Retention wise, I have a feeling it'll be Martin that departs. Can't be a lot of wriggle room on the cap which might see King stay and I suspect Hurrell will be offered reduced terms for a couple of years. Suppose it depends what other offers they both have on the table- both would likely get a first team spot in SL and I think Hurrell played RU at the start of his career so maybe that's an option for him too.