There is way more downside risk to this strategy than you are mentioning. You don’t just lose a portion of the gain. You lose a portion of the whole enchilada.

I don’t think your plan is a terrible idea but entry point is key and stocks valuations are pretty stretched. If your 100k turns to 50k from a market pullback you will then only be making 8% on half of what you started with. Yet you’re making principal and interest payments on the original full 100k. Be careful.