How much do you plan to use the scaffolding once you get done with the current project? If you only need it for a couple of days or weeks, look at renting it. Cheaper and you don't have to store it until the next project comes up years from now. Depending on the type of work and amount of it, you might want to look at renting a small electric manlift. If so, make sure you get non-marking tires for it.
I'm in a similar situation as you. From what I saw on all of the various websites, if you stack this type of scaffold, you need the outriggers (about $100) and a set of guardrails (about $150) to make it safe. The one question that I have and can't seem to find an answer to is if you have the upper platform set below the max height, do the guardrails fit around the uprights that are above the platform?
I have a 14'-6" tall foyer that needs to be painted, have crown molding installed, and have a new light fixture hung. My thinking is that I can always find a use for scaffolding here - lighting in the family room, lighting in the garage, outdoor work, plus whatever my relatives want to borrow it for but do I want to tie up several hundred dollars plus all of the space it takes to store it in my smallish 2 car garage.