Thank you. The secret to less air bubbles in the buttercream is to keep your buttercream at room temperature and in the warmer side. This way, when you press on the buttercream again the cake, it kindda squeezes out any tiny air pockets trapped in the buttercream. When your buttercream is on the colder side, it is harder to spread it giving it lesser chance for air bubbles to escape. If your bc get too cold, just zap it for a few seconds in the microwave, re-beat it again with a paddle attachment and proceed to finish your cake. Pastry is about fun and imagination. I like thinking out of the box and adapt desserts and flavors not conventionally or traditionally done. Sometimes, you can use lavender honey or rosemary to perfume your custard filling other than the vanilla, chocolate, and mocha flavors.
Happy Baking everyone