You can find detailed guides for fishing - both for members and for free-to-play - and similar guides for other skills, at online sites such as runescape.wikia.com or others.
The best way to fish on runescape is to use a net or a fishing rod and bait in draynor. Then it is easy to bank your fish
From Runescape Wikia: "The Cavefish are a type of fish that can only be found in the Living Rock Caverns. The Living Rock Caverns can be found underneath the Dwarven Mine..."
On the pier in Karamaja ;)
Raw fish.
There are various spots throughout all of runescape you can harpoon fish, the main ones are catherby, the fishing guild, and the island of karajama
Bass is a members only fish, only members can fish it.
No. In runescape, there are lots of places you can fish swordfish.
You need level 30 fishing to fish salmon.
80+
Rocktail
Yes.
no