I think the odd one out will be Aitken to be honest, his size and lateral defence are deficiencies in his game that other teams are exploiting.
I thoughts are:
F/B - Dugan
Wingers - Mann and Nighty
Centres - Milne and McDonald
5/8 - Hutch/Widdop
7 - Widdop/Hutch
For 2018 and assuming Herbert develops well with the Cutters, he would take Nighty's spot.
Milne, as someone has already mentioned will need to improve his defence in 2017, lucky he has Nightingale but in 2018 (assuming) with Herbert he will need to step up and be senior. In that case I would sign Levi Dodd, who is quick, defends well and scores tries and kicks goals as a shadow if Milne doesn't cut it or gets suspended (given his apparent likeness for shoulder charges).
Young Aitken needs to re-invent his game, too small for a centre now, maybe a bench rotation player, to play forward or back, the only problem we have a few of those already.