I'm not going to look up the specific lenses and stick to general advice you can apply to your choices.
The 100mm is great, I've had the EF version for many years and use it with an adapter. It is macro but it's macro light, you're not going fly eyes with this alone. And while it's a great lens beyond just macro (great for portraits, product, anything where you need a mid-length telephoto really), it's definitely gonna limit you if it's your only lens and you're on a crop.
So maybe macro tubes, these shouldn't break the bank and will transform any lens into macro (bit more finicky than using the 100mm though!)..
But then you still need to choose the focal length for your prime, and there you have somewhat opposed requirements. For macro you don't want too short, because even if the tubes let you focus very close, you don't want to have to stick the lens right next to your subject lest you'll introduce distortion, spook the living ones and/or cast shadows with the camera on it.
So while I'd normally recommend 35mm full frame equivalent as "the one prime" if your main goal is macro you probably want significantly longer... It's up to you, just keep in mind that while you're telling yourself you only need one lens for now, that's not gonna last and you're definitely gonna get more down the line ;p