Well, there is a little detail about the portal you might want to know: It works one way. As in, they can come into your dimension but you can't enter theirs. So you will need to let them enter your world, build up a camp, and wait as they build up. Then you need to sneak into their camp and steal the resources(Running in,sword swinging will be a horrible idea and Way has plans to make it even worse, like alerting one demon will agro the entire camp, start spawning guardian demons, and halting all expansion and resource collection for a time if your spotted). Building hidden tunnels or teleposer networks will be the ideal way to go about it.
As for opening the portal itself, Way has a few ideas over how that will be done. A sacrifice of an innocent and a load of reagent is the current game plan.
If Way were to add a dawn rune, it wouldn't be a T4. In all likely hood, it would be a T6 thing as to gate of rituals using something other then LP cost.