Hello! Let me see if I can at least answer a few of these points real quick.
That's still in the initial plan for plant gathering. Right now, the quality of mats collected from plants are either common or rare depending on the plant but this may (or may not) expand to include all quality tiers in the future. The current amount yielded on harvesting is pretty consistent for all players at the moment, but could potentially change if the reaping skill becomes trainable.
So this is an interesting question and I'm curious to know what feedback I'll get after I answer this. Initial