Rubygems is a package manager for ruby libraries, so you need to install ruby before you can install rubygems. RVM is a great way to install ruby and will in addition install rubygems for you. Once you’ve got ruby gems you can then install rails.
Ubuntu Desktop works just fine. Editors are quite a personal thing, although at a basic level you are just editing text files, so any editor will work, although some will have features that may make your life easier.
Rails is primarily for writing web applications and (at least that’s my first impression) it doesn’t sound like you’re writing a web application. Ruby itself is a fairly general purpose language and may well be good tool to use.