Dunkley will be role dependent but for me he's the "must start" of he and Duncan.
Dunkley in the right role is a genuine 120+ guy, huge hurt factor if you don't have him. If the position looks all off he's worth shading but if it doesn't then I think you just have to start him.
As good as Duncan is, he's pretty fairly priced on his last 3 seasons and has had a solid downward trend in both points and games played over those 3 years, especially compared to his previous couple of years. Duncan for mine shouldn't move in price. There are a couple of roles he could shift to that might alter that feeling but for me he's a solid 95-105 guy and will be priced in that range all season.
I have Butters the lowest of those 3 but I do love him as a player.
I think Heeney is a legitimate 105+ candidate this year with the role change, if Mills is out early or underdone that just becomes even stronger. Durability will always be a concern but he's ~15 points on his 4 year average so he's just got too much proven upside to care about that if his preseason remains excellent.
Thomas I think is more of a 95-105 guy although there's definitely a 105+ guy in there, just think it's another year or two away but happy to be proven wrong on that. The way he finished last year he made 100+ look kind of effortless, there wasn't anything he was doing that was unsustainable to me and, if anything, there was room for improvement. His role needs to be monitored with lots of changes at North but he's too talented for them to push him to the backseat, imo, for basically anyone else they've got.
Butters the durability last year was a concern and he's definitely the least proven of the 3 for scoring, having never really done the whole 95+ for a season or even half a season thing but he's shown the ability to score huge last year (163 and a 96 that scaled backwards from half time after being injured). Role is everything but in the right one he could be anything. He's a lot harder to put a range on for me because I genuinely have no idea what role he might play and even if he does have one it can change at the mercy of musical chairs Ken.
I love several other guys in that price group as well including JDG, Stringer, Bolton and Graham among others to all be potential 100+ guys this year. God I'd feel dirty picking that latter group though, which means they're probably the ones and I'll look stupid taking the ones I like