1. I haven't tried farming quarry bushes yet, but I checked and quarry bush leaves are missing the [EDIBLE_COOKED] tag on the leaves. The baseline leaf entry is also missing it, so it just doesn't get the edible cooked tag. You could add it in either the leaf material template (which currently only affects quarry bushes, since they're only one using that template) or directly to the quarry bush entry.
Heres the quarry bush entry with the tag added in
red:
[PLANT:BUSH_QUARRY]
[NAME:quarry bush][NAME_PLURAL:quarry bushes][ADJ:quarry bush]
[USE_MATERIAL_TEMPLATE:STRUCTURAL:STRUCTURAL_PLANT_TEMPLATE]
[MATERIAL_VALUE:2]
[EDIBLE_VERMIN]
[BASIC_MAT:LOCAL_PLANT_MAT:STRUCTURAL]
[PICKED_TILE:5][PICKED_COLOR:7:0:0]
[GROWDUR:500][VALUE:2]
[USE_MATERIAL_TEMPLATE:LEAF:LEAF_TEMPLATE]
[MATERIAL_VALUE:5]
[EDIBLE_COOKED]
[LEAVES:quarry bush leaf:quarry bush leaves:7:0:0:0:0:1:6:LOCAL_PLANT_MAT:LEAF]
[USE_MATERIAL_TEMPLATE:SEED:SEED_TEMPLATE]
[MATERIAL_VALUE:1]
[SEED:rock nut:rock nuts:7:0:1:LOCAL_PLANT_MAT:SEED]
[SPRING][SUMMER][AUTUMN]
[FREQUENCY:100]
[CLUSTERSIZE:5]
[PREFSTRING:gray leaves]
[WET][DRY]
[BIOME:SUBTERRANEAN_WATER]
[UNDERGROUND_DEPTH:1:3]
[SHRUB_TILE:58]
[DEAD_SHRUB_TILE:58]
[SHRUB_COLOR:7:0:0]
[DEAD_SHRUB_COLOR:0:0:1]
You could also add [EDIBLE_VERMIN] if you wanted the leaves to be edible by vermin (I think it was in the last version?). I haven't tested this but it should work.
-edit- I also just noticed that the seed template doesn't have edible cooked tag either, which is why seeds are no longer cookable.
2. Not sure. Seems about normal to me, but I never really paid much attention to how fast lava flows.