Ignoring why you want to expose a device to the internet with an IP, instead of opening only the necessary ports via NAT,
you have not explained how the provider delivers you internet and how they should deliver the second IP to you.
Paste this on terminal for join ether1 and ether5 on one bridge, starting from default config is required.
{
/interface bridge
add admin-mac=4A:A9:8A:00:00:01 auto-mac=no comment="rexconf undo: delete this" name="bridge-WAN"
/ip dhcp-client
set [find where interface=ether1] comment="rexconf undo: set interface=ether1" interface="bridge-WAN"
/interface bridge port
add interface=ether1 bridge="bridge-WAN" comment="rexconf undo: delete this"
set [find where interface=ether5 and bridge=bridge] bridge="bridge-WAN" comment="rexconf undo: set bridge=bridge"
}
And about firewall, since on bridges the firewall is not used, for default, is all allowed between ether2~4 and wifi1~2 and separately also between ether1 and ether5.