I've had my Ares for a couple of months now and love it. My coils are 27 or 28 gauge SS round wire and they mount quite easily for me. There is IMO also enough room in the mounting slots for multiwire coils like Claptons, square wire setups, etc.
DJSlb Vapes has posted a
really good video review of the atty and how he mounts these coils. Go to minute 48:20 to see how he does it for the Ares. You can also see how comparable atties work in that video.
26 gauge wire will be easier to work with than my thinner wire. You do need to take your time at first to get the hang of it, but once you get it it becomes easier and easier each time you repeat the process. IMO buying premade coils will not help you do this, it's just a matter of practise. SS and Kanthal doesn't matter here, they handle a bit different in my experience but not much. A coil is a coil, weather you make it yourself or have it made for you. If you are having a hard time wrapping a coil that looks like his that's another issue as opposed to mounting it and we can help you with that if that's an issue.
Good luck with it