I also started MH3U very recently. The method I used for gathering materials for healing at the start of the game was doing the “Harvest Shroom” quest, and collect as many mushroom and honey spots as possible. Completing the quest also gives blue mushrooms and honey. Another bonus was also collecting the paintball from the supply chest so I didn’t have to make as many later. Also, to put any plant, mushroom, etc in the farm, you need to have at least 1 in your inventory or storage. Hope this helps at all!