In ethernet interface configuration, set ether8 as master=none and ether9 as master=ether8
Also set ether2 to have master-port = none, and ether3 - ether5 to have master-port = ether2
On ether8, create vlan interfaces
Put IP addresses on each vlanX interfaces where you want the Mikrotik to have an IP address in that vlan.
Any vlan that is only passing through the Mikrotik as a switch, you won't need to make a vlanX interface for that VLAN.
vlan100 is the exception put no IP address or dhcp or firewall rules on this interface - and you need this vlan interface for the next step even if the Mikrotik won't get an IP in vlan100.
Finally, make a bridge called bridge-vlan100 - put the IP / dhcp / firewall rules / etc for Vlan100 on this bridge interface.
Connect ether2 and vlan100 interfaces to bridge-vlan100 as ports.
This will do what you want.
When given a spoon,
you should not cling to your fork.
The soup will get cold.