You’ll want to fill each of the pans 2/3 – 3/4 full so you may have extra batter leftover if you’re only filling 2 pans instead of 3 (you could use the leftover to make some cupcakes or something). Since you’re doing less layers as well, you won’t need the frosting in between one layer, so hopefully you’ll have plenty 😉 I’m not sure how cake flour will work, but it should be okay, I haven’t tested it though. Let me know how it goes for you