The centrifugal force isn't real, it's only an observed force when you're inside the rotating frame of reference. A constant force does still have to be applied, it's just often an internal force, not an external one. In the case of an object rotating in space, there is a force of tension acting in the outer parts of the object pulling them back towards the center. Due to that the object will stay in rotation without any outside force, but the key term there is outside. there still has to be some force to keep an object rotating, it can just be an internal force. That internal force (as I said, the force of tension for an object rotating) is the centripetal force.

Those internal forces are what I meant, as such the object is still technically accelerating

Well yeah, as I said on small scales it does seem to be inertial but it isn't quite and those effects are noticeable between multiple objects in similar orbits.

Wouldn't an orbital frame not be inertial? I mean in a small scale it would appear so, but an orbital reference frame would be the same as a rotational frame which is non-inertial. That can be proven by the fact that if you stick two object close to each other in orbit, they will drift around from where they were relative to each other. That wouldn't happen in a fully inertial frame of reference.

Yeah, the earth is accelerating, exactly in the direction of the sun. It's falling towards it, but it's momentum keeps it from actually getting any closer. Even though the earth has reached a kind of equilibrium where it will stay in orbit, its still constantly accelerating towards the sun.

Linear movement continues without any force, however rotation needs a constant force to continue, that being the centripetal force. Seems odd because a force doesn't seem to be applied to a spinning object in space, but technically there has to be some force on anywhere outside of the center of mass, likely some sort of tension force (or in the case of larger objects like planets, gravity).

Edit: I want to clarify that that necessary force isn't necessarily external. A rotating object will continue rotating without an external force, however within the single object, particles near the outside of rotation will have a force of tension pulling them back towards the center, which is also the centripetal force. If that force didn't exist, the object would break apart.