Once Super Saiyan, does Kaioken only come back once a Saiyan attains Super Saiyan Blue form? Or can the Kaioken be fused along with Super Saiyan at an earlier stage than Blue?
No, it's still usable in standard Super Saiyan form.
While it's seldom seen after he attains Super Saiyan form, Goku actually uses the kaio-ken while in super saiyan form in the Other World Tournament against Pikkon. As Goku is not limited while dead in the same way he is in life -- he is already dead, so he isn't in danger of dying due to the kaioken, and he is able to exert far more power, as he later explained when he transformed into Super Saiyan 3 form -- it's likely that this is the key to allowing him to combine the super saiyan form and kaioken techniques.
It is important to note that the Other World Tournament is an anime-only filler arc, but was alluded to in Super, and thus may be within Akira Toriyama's canon.