Yes
Yes, Castle Wars is a members-only activity.
You can only make an army whilst playing clan wars (Non-members) or castle wars (Members)
Bandos is
No. Clan Wars can be accessed and played by all players.
They are first at the cosmic rune altar, then the farm below falador, and the ogres or on a members server, east of castle wars.
Buy it on the Grand Exchange, or earn it in God Wars Dungeon
yes it is members only
You use a "Games Necklace" to teleport to "Clan Wars".
I have posted a link below in the "Related Links" section that may be useful to you.
The God Wars Dungeon is full of monsters ranging from level 11 - 600+. Its very dangerous but the rewards are good and can earn you up to 100m+
Runescape god swords are in fact for members but the closest weopan you can get to a god sword is the dragon 2h sword. the most expensive god sword is around 50 million gp.
it is really impossible the best way is the god wars dungeon really