About items on floor, why not have the item's background transparent? It would just display the normal floor tile under the item... that's how ToME and Angband, for example, do it.
Libtcod replaces tiles. Floor tile is replaced with the item's tile. There are no layers basically.
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Little info about monk gameplay:
stunning palm can be used only when unarmed,
circular kick can be used when armed but there's no bonus from being unarmed,
pain tolerance reduces taken damage by 1.
These skills favor unarmed melee combat but anybody can play it like they want.