Subscription fees work a little differently to All Or Nothing campaigns, so here's the go;
Platform fees won't be charged until your profile has $100 or more in subscriptions per month. Once you start earning AUD$100 or more a month, you'll be charge 5% of subscriptions/month.
Merchant fees are Stripe's fees. You'll be charged 1.75% + 30c/pledge, and then varying fees depending on your payout schedule. See more here: https://stripe.com/au/pricing