its too easy
1- active dmz in the nat on your isp modem to wan ip on mikrotik
2- disable firewall on isp router
3- add line as the sam you see on Access Management >> ACL >> Lan but add other one as WAN on ISP rourer
What happens if you connect your PC, and possibly another test device, directly to Eth 3?
yes i used that and network become fasthttp://wiki.mikrotik.com/wiki/Manual:Wiki/Fasttrack
I believe this is enough.