The point is you dont have to create a subnet for the WAN traffic, just create a vlan, which will carry the data to the 5009.
Untagged port at the switch on the port to the ISP modem, added to the trunk port going to the other switch, added to the trunk port on second switch coming from first switch, added on trunk port going to the 5009, added to trunk port on 5009 coming from second switch. Terminate the vlan on IP DHCP client on the 5009, done!! Use ether1 for an oFFbridge config access safe point.
If you are planning on using vlanid=1 then you havent learned yet the MT vlan filtering, suggest this document - http://forum.mikrotik.com/t/using-routeros-to-vlan-your-network/126489/1
I have TP Link switches, netgear, dlink, all work fine and all have native vlan1, but this is NOT the management (or trusted) vlan, nor a data vlan, just sits in the background.
(on switches, it typically remains an untagged member off all trunk ports, and has no affiliation with access ports)
I dont work from screenshots but happy to review a proper config export
/export file=anynameyouwish (minus router serial number, any public WANIP information, keys etc.)