Since you're using prowlarr, I recommend adding as many as you can. You'll get some stall, but that's the price you (don't) pay. If you have the time, choose several baseurls for the failing indexers so you can get as many as possible.
It can feel like a lot of money up front, but it really is just up front. If you consider the subscription services and compare that to the life of your hardware, you're in good shape. With the amount of media we consume, my family has paid it off months ago.
I'd trade my writing skills for coding skills. I feel like I'd be happier programming than teaching kids how to write.