You'd have to use something like 12-14k gold to get near enough hardness, and it would still be soft. OTOH, it's a pendant, so it isn't under any heavy use, like a bracelet or a ring would be. It's pretty well protected, just hanging there on the chest.

I understand the sharp outline you get from cutting, but you still have to file and polish those edges anyway, and that's what gives it the sharp outline. You could still do that in a cast piece. In fact, you'd probably have to.

Casting is pretty easy for small things, once you get the hang of it. It's not something you'd want to do inside an apartment, though. Definitely an outside activity, unless you're already in some sort of industrial building. It's fun though, and it feels really good to show off a cast piece. That's an impressive skill to outsiders.

BTW, I'm not a jeweler, but I have a close friend who's a pro, and I spent many hours sitting next to him at his bench, poking through his little drawers, and asking questions, and occasionally crafting my own amateurish pieces. I used to like to carve wax models and cast them in silver, back when silver was dirt cheap. Fascinating stuff.