I'm not sure about performance but lots of custom 1911 shops build 5" open guns so I suspect the performance will be fine. You will probably have to do some tuning to work with your ammo and make it perform for you. They will need to do some blending between the comp and the slide. Depending on the comp you select, it probably isn't going to look much different that the current Chaos 2 but with the slide going to a full 5" and the comp extending from that.
As for the barrels, I see them in stock at Cheely and it seems KKM is taking orders again for 1911 barrels. It is just a regular 5" Government 9mm Threaded Barrel that has 5.4" OAL.
I would imagine the Artemis with a second barrel fit with either a single port comp like the Erebus or a multi port comp like the Chaos depending on what you like. I would really think about what you want to shoot as the Chaos generally does not function well with minor PF ammo for Steel Challenge. I get a lot of unburnt powder thrown back at me when I shoot minor and it hasn't been 100% reliable so I just shoot my major PF ammo for Steel Challenge.
I suspect there is going to be a lot of custom work necessary to do this and I feel at this point, Atlas just wants to churn out guns and not do any one off custom work. If you want a custom, you are better off going to a place like Venom where Don will work with you on the design.