Unfortunately the items is not account bound. How I wish this game would be more alt friendly...
The respawn is same as other mobs. By time you do a full circle of the field, they should have respawned.
My FM with 470ap can reliably kill the Bear, Bulbari and Thrasher without dying. They dont use any high damage skills.
The Grassquatch and Fire/Ice Bird might need more AP/DPS to kill it at a faster rate.
The drop rate is truly abysmal. I got lucky on the Thrasher with first kill drop. Still need the Root and Honey, killed 50+ combined and still nothing.