In season 1 episode 23 of the anime, at the end Rimuru creates a golem and summons a demon to possess it. It's his way of repaying Ramiris for her golem that he destroyed. Could he make a large number of those golems, even mass produce them as workers to fuel an industrial revolution?
Yes. He needs magicules to summon the demon, materials to make the body (for Beretta he made it out of pure magisteel), and the demon needs to agree to the contract. If all those requirements are fulfilled, he can make as many as he wants. Both Beretta and Diablo he paid generously one way or another and they both wanted to serve him permanently.