I have around 100 Iridium-quality Chubs at that point for eating. Ideally you don't want to eat too many, since you can sell them, but ghosts deal such little damage that I don't think it matters much.
Right, so I fish less than you do, and that leaves me on about 20-30 iridium chubs at the point where I hit the ghosts... Just enough to get far enough through the mines in time for making my quality sprinklers. I don't see that as infinite energy, but I see how your version would be different.
I'm just trying to envision you sitting in the mines and swinging at a ghost with Steel Smallsword 16 times in a row. It doesn't sound very productive. =p
No, it isn't! :-) But it doesn't normally happen. Normally I get a better weapon, which makes a huge difference. The odds of getting a Forest Sword or even a Neptune's Glaive are really quite high.
I obviously never want to sit there swinging with a steel smallsword. But if it's just for one level, and there are dustmites, bats and grey slimes to kill at the same time, it's not so awful. If you are on spring 7 or 8 and haven't upgraded your pickaxe, it can be a thing...
Absolutely not! In the Skull Caverns, you do the exact same strategy that you do in the mines - ignore all enemies. You can't really ignore Serpents though, so you end up killing them. But note that killing Serpents is pretty fast, whereas killing Ghosts is excruciatingly slow. So you should be picking more wisely which enemies that you are killing for XP.
I would never choose to kill ghosts for xp. I kill them because otherwise they get in my way whilst I'm trying to break rocks. Which is down to me being earlier in spring than you and having upgraded my pickaxe less. A choice I stand by, I think.
My comment about combat xp was based on the fact that you said I should get combat 10 in order to get large amounts of money from skull cavern. So in that case I can't ignore all monsters.
When would you expect to get combat 10?