There is one bank on almost each of the main isle on both HorseIsle 1 and 2.
There are approximatley eight banks on HorseIsle 1:
There are also eight banks on Horse Isle 2:
2
Three.
There are seven of them.
25
You can find Papyrus plants (which can be made into paper) grows on the banks of the ponds and near the pyramid mini-games, on desert isle.
There are many good HorseIsle guides for both HorseIsle 1 and 2. Unfortunately, many HI1 guides are out of date because the game has lost popularity. View the Related Links section below for some handy links.
1-4
at least 2
See the question: What are some websites with Horseisle quest help? It currently has too many alternates. Also, websites are not allowed in answers.
There is no actual way to hack into HorseIsle.
HORSEISLE ANSWER:SpiritEverPuppy-Brown Server
Horseisle is a computer game so it is international.