Only read OP, going to post, then go back and read, but I see two forms of implementation here.
Auto-attack is a toggle for on/off in the Options menu and with some kind of keyboard or gamepad shortcut. By having it on, whatever 0 TP attack skill you choose at the start of combat (or switch to during combat) becomes your Auto-Attack. And it doesn't spam the Stamina bar, so it will attack, allow for time to replenish the stamina bar, then attack again. This would allow other stamina actions to be used, allow the player to type without feeling like they're doing nothing for the battle, and when the player is ready to take control of their stamina, they toggle off AutoAttack and do the spammy thing they do.
Second implementation which would require some overhaul: Keep the stamina bar, make it regen slower. Choosing a 0 TP attack becomes your auto attack until another ability is chosen. Its attack speed is based on the old amount of stamina it used to consume. So Broad Swing auto attack would be slower than the standard attack. Slow would reduce auto attack speed. Haste / Speed Surge would increase auto attack speed.
In regards to voice chat, it may be a nice option to implement in-game, but I don't see the majority of players using it, even if they have mics. I'm only basing this off of Steam games where voice chat is built in and only four to five out of twenty players will talk. And from Xbox Live, playing a non-FPS game, you may have three out of eight players willing to use their mics.