In addition to the guide to VLANing on ROS you might want to read this article: https://forum.mikrotik.com/t/routeros-bridge-mysteries-explained/147832
It'll help you understand different properties of bridge.
And: the beauty of ROS is that apart from most advanced stuff every device can do everything (albeit some of devices will do it slowly). So you can use your RB450Gx4 and try the configuration (exactly the same variant as should fit RB5009) of VLANs.