FatherGhonel,
We currently raid Thursday and Sunday nights from 8 pm to 10 pm EST. Currently, the Thursday night raids are open and the Sunday night raids require higher levels of DPS and healing (generally we have 3 competent tanks).
You may also want to try Mythic+ dungeons with a STC group. With a level 10, you can get an 880 Item Level piece. We have groups who go multiple times during the week.
You can do a "/who Sanctus covenir" and try and find Gerhart or just ask someone who is on if there is an Officer who you can speak with. Officers can do a guild invite.
We have not tried Discord. I know very little about it. We are always looking for alternatives to paying for a service. If you have info, please share with us.
Mumble login information is available in game under the Guild Info tab.