Unfortunately when I downloaded the manual for the first generation Katana it states it is not compatible with speakers that the input impedance is less than 8ohms, Kones are 4ohms so I'd advise against dropping one in.
If you have an interest in the Kone I would recommend a Kabinet, since you have the stage there's two options, a class D power amp plus an unpowered Kabinet or make it easy and get the powered Kabinet.
If you already have an empty speaker cabinet and power amp then putting a Kone in that would save money, if not I think a Kabinet is the best option. One thing I found with the Kone, it sounds better with some volume, at lower volumes it didn't sound as good to me but that's just a personal observation, others may have different experiences and opinions concerning this.
As far as studio monitors, I have a cheaper small pair that i use for some video editing, the Kemper sounds terrible through them but I have no intention on doing multi track recording again as I once did so I see no reason to spend money at this time for a better quality pair of monitors.
I also have no intention of plugging my Kemper into a pa system so I went in another direction for monitoring, I have it setup more like a traditional amp but one that is more versatile beyond anything else I could imagine using, but that is conclusion I reached based entirely on personal taste.
Most of the users on this forum have reported great results using good studio monitors (and a good recording interface) as well as with the Kabinet or powered pa speakers, I'd say my experience is in a much smaller percentile of users. But looking at your original post of intended use I would focus on studio monitors, there are multiple discussions on the forum on this subject,. Take some time to read through them as you'll probably find answers to questions you have concerning them already answered, if the information you need isn't found then fire away with your question, the members on this forum are not only helpful but very knowledgeable.