The creator of this nice little mod doesn't come online much, (it's been 9 months) but I do believe he will get a notification if you send him a private message. Otherwise I'm afraid you will be waiting long for an answer.
And it has been a long while since I played this mod myself. So I can't really tell you. Sometimes you just need to backtrack or go talk to the white rat npc to progress to the next stage. Or offer items to npc's. Manually drag items to npc's, don't use the sell option. The figurines are offered to the talking skeleton commander if I remember properly. The fact that you haven't found the Ogre figurine yet, basically says it all. That little fellow can be found on the very first map you start out and requires nothing but simply killing the ogre. Check your maps more carefully and navigate through foliage.
And I think if I remember correctly, the power gems can be placed on altars and alcoves. Every time you encounter an altar or an alcove, just place a power gem on it in case it needs one. They are also actually currency to upgrade weapons and armor if you find the blacksmiths.
The skull key is actually used in the same teleport maze where you found it I believe.
The mod isn't hard progression-wise. And it doesn't really have "impossible to find" progression blockers. I finished it completely without any help/spoiIers or hints needed. I would suggest to look at your maps very closely to check which parts you haven't explored yet. That should probably put you in the right direction.
And read about tips/spoilers in this topic. You should find your way about