Our guild has gone through a few different things in Pandaria and WoD (which has been my time as guild leader) and there are a few lessons I've learned along the way that will make me change how we do things in Legion.
In MoP we had Saturday fun nights, and in WoD we had Sunday normal runs (and in this lull before Legion we're doing heroic casual runs on Wed/Thurs but that's not a permanent thing). As a guild that has members who are heroic focussed and those who are more casual it's actually quite good to have separate raids where they can feel comfortable playing with like minded people. Heroic raiders are welcome to come to the normal raids as long as they realise that we will be teaching them the casual players the fights as well and patience is to be expected. I quite like how this has been going, and I will continue it in Legion with Heroic raiding on Wednesday, Thursday and Monday and casual raids on Sunday. However in the early part of Legion raiding we'll do Wednesday, Thursday heroic raids and Monday casual raids as we won't be progressing super fast in early Legion and doing some normals may help with gear as well.
There was a massive explosion of people who wanted to raid when we started in WoD, so much that we had to sit people out and take turns - and tons of these peeps did not come back to raid. Who is going to get to go to heroic raids? I think that anyone who has been doing mythic raiding with us in WoD should get into a heroic raid, and everyone else will have to go through casual raids first and see how their performance and their raid awareness goes, as well as being "ready to raid" in terms of flasks, pots, gems and chants. We will also be stricter on required addons for heroic raiding, and Discord will be a must. And there will be no putting the raid leader on ignore because "the addon whispering me that I haven't eaten food or flasked is annoying me". Oh man, Kyxyn was absolutely ropable when that event occurred with a raider!
We have usually let a number of people raid with us who are not from our guild, and I have looked at them as pseudo-guildies. However, in the early part of Legion we have probably not have any PuGs because it will be stuffed full with guildies who have returned to look at the new expansion. However, as the shininess of Legion wears off there will be room for regular non guildies to come again so I have a feeling that will be after.... 6 weeks! Shall we take bets?
EPGP was the loot method we used for the whole of WoD and later Pandaria, and to avoid drama in the future, we're going to go to personal loot. Personal loot also means faster pulls, and less time wasting. With the ability to trade duplicate personal items of loot it might make it a lot easier as long as people actually keep the unwanted item in their bank somewhere. The opposers of personal loot have actually been the ones who complain about loot the most when it is distributed with master loot or rolls, so eventually everyone is going to get used to it.
I used to tell people we needed X melee or Y ranged, and then we didn't need them, and when someone asked if they could heal I told them we have too many and now we are short! So I have decided that everyone should play what they WANT to play, however, if fights struggle then we may have to drop people if we had too much melee or healers. So far, for heroic raids, I have two tanks - Kyxyn (prot pally) and Aimei (Brewmaster Monk) - Me (resto druid), Koda/Cosima (resto shaman), Bish (holy priest), Sev (affliction warlock), Lushen (windwalker monk), Aza (destruction lock), Crooked (shaman), Splatz (DPS warrior), Sars (Enh shaman). I'm not sure what Ultra, Exray, Dan, Rag, Duck, Voe, Neuro are going to play. And also not sure if Fielsa, Gorvek, Naesca and Mauve are going to want to raid heroic either. But at least we have more than 10! Will there be 4 demon hunters? Who knows!
I am excited however, thinking of new raids, and playing with our old friends! And maybe some new ones? Oh so much more to look forward to!
We've always used the "play what you want to play" option - but we're more casual than you guys. I do try to encourage people to have dual spec - primarily tanks and healers - because it makes it easier to plan and organise raids, especially if we suddenly have 4 tanks wanting to come along!
We had a massive influx of returnees and new members at the start of WoD, nearly 50% of whom just drifted away after a while. I don't THINK we'll have a problem with too many people to raid, but if that were the case, and we had a set team, I'd certainly give priority to those who have stuck with us throughout the expansion. It seems unfair to instead give their space to someone who is just a fair weather raider.
We've been Personal Loot for a while. I know currently it has its down sides, but for casual raiders it made things a lot less "drama-ry" - not that we ever had any major drama over loot - but you're right, it's a lot faster with PL.
Discord is a free voice chat - much like skype. It's free and it has great functionality. You should try it! I moved to it because it was free and I like that it has attached chatter channel you can type or put links in during voice chats.