Here is a tutorial on HIM use. I’m guessing that the component itself has an AddInstance() method that will help you place your houses. (I have not used HIM)
However, 1000 blueprints is not a massive amount of polygons so it should not have such an impact on your performance. (unless each house model is tens of thousands of polygons in which case - this is the problem) Reasonably current GPUs render tens of millions polygons without breaking a sweat.
My guess is your house blueprint uses many materials and has no LODs set. This will hurt your frame rate.
Check this article by Bob Cober for additional optimization techniques. Although a bit outdated, it still explains the most impactful and widely used graphic optimization techniques.