itch.io

1) I think you lose to her if you want to advance the slime girl quest line. Honestly you can just try both options. You can't permanently kill the slime girl so even if you defeat her, you can just come back later and lose or surrender to her on the next attempt. 

2) Just keep buying stuff from Lucas. His sister will eventually show up.

3) I don't think there's any more info from the stone. At this point i think it's just used for the cat. (I could be wrong though, since I haven't finished the latest update yet.)

4) Don't think so yet. (see previous answer though)

5) Pretty sure you can't do anything with magical beans yet. Electric shard is used much later in the game (after you find elf village) to acquire an AoE spell. 

I don't remember exactly where they are, but you are looking for fusion items with name like "X stone".  I think the 1000 gold wallet uses a "turquoise stone", and the even bigger one fuses with a "ruby stone". I think they are found in chests in late-game areas, but I don't remember exactly which ones.

It sounds like you're still pretty early in the game. I'll try to help you as bests as I can remember since it's been a while. 

For the cat:  At some point you open up the jungle-like area south of the forest, called Palmtree Spot or something. It's the zone with the jellyfish that can paralyze. Explore that area until you find the Fisherman's dock. Help the fisherman by giving him one of your items (hint: you mentioned the item that you need in your post). He will give you something to feed the cat. 

For the ghost: This one I don't remember exactly. I know that early on the ghost only appears at night (try after midnight. You might need to use an energy potion to stay up long enough). Early in the game you also need to have the spirit stone equipped to see the ghost. If you don't have the spirit stone yet, talk to Evie (I'm pretty sure she's the one who gives it to you). 

Yes. As far as I know it's not possible to permanently kill the demoness. Come back to the area on a different day and she will eventually respawn and you can fight her again. 

In order to complete the quest(s), you do have to lose to her at some point though.

Yes, most of them are drops from the rare chests in various areas.  (However, I think I got one of them during the Capt. Ceres quest)

I don't remember exactly how to get the charm spell. I know you get it from Selena at some point. I think you need to finish the toy maker questline first, (where he makes his doll wife Candy after you feed the cat in the plaza). After that, Selena will ask you to find a locket or something in the toy shop. Talk to the doll to get it, then Selena will give you the charm spell. (I might be missing a step here or there, it's been a while.)  

To first encounter the demoness, you need to explore the dark woods with Evie in your party. Keep exploring and you'll eventually get a cut scene where you find some ruins. 

After that, you can encounter the demoness again by exploring the dark woods (you can do this alone now if you want) until the forsaken keep area opens up.