I'm creating a multi-step form with pagination that will show a Next and Previous button depending on which step you are on. In order to display the buttons correctly, I need to store the total number of steps in a variable somewhere.
Do I store this in the Request scope e.g. REQUEST.TotalSteps = 5 or Application scope e.g. APPLICATION.TotalSteps = 5? The number of steps will rarely change so I'm thinking that Application scope is better suited, but I want to minimize the use of RAM because I have a lot of stuff stored in the SESSION scope for each other.
What would be the ideal option?
Depends on how you're gonna be using it really, and what framework you're using, how you're architecting your app and all that sort of thing. You only need the value in memory during the request(s) that need it, so TBH I'd just put it in the variables scope, making sure that the code that sets that variable is loaded for the requests that need it.
You'd not want to put it in session because it's not value specific to the visitor, nor does it have any relevance to the session: it's all just about that form.
Similarly it would not belong in the application scope (well: that has caveats, but given the low level of detail you give us as to how you've built you're app, let's assume this to be the case) because - again - it's not something the entire app needs; just the pages actually interested in how many pages that form has.
If you can give us more information regarding your architecture, I can possibly fine-tune this answer, but based on the info given: this is pretty much how you need to approach it, all things being equal.