There's plenty of fish in the sea, kinda? No, not that I know of. (Det er flere fisker i havet, BTW)
No, just "skip". Like other monosyllabic neuter nouns, "skip" gets no added ending in the indefinite plural.
Is it just me who struggles to pronounce 'vn' in Norwegian? I find it so hard to say right! I never see anyone talking about it though, so I feel like it's just me. I've tried to think of an example of 'vn' in English words which I could Norwegian-ify to help me pronounce it, but I can't think of any. Any help with this?