14 yo stepson just diagnosed

I need some guidance. My son (not biological, but he’s my son) just got diagnosed with ASD. He’s higher functioning, doesn’t need much in the way of supports. But he manifests in his particularities around things and his stubbornness. 

Everything I’ve read encourages consistent rules. My wife wants to be really flexible with rules and I’m struggling with this. The doctor who diagnosed says to lower expectations and resetting after getting started with a collaborative approach to parenting. I’m concerned about changing things until we get some professional guidance. My wife wants to plow ahead with lowering expectations now though.

please help with guidance