Going from a 6 gal carboy to 1 gallon jugs is a little unconventional, but I dont see why it wouldnt work. If you have the gallon jugs and havent pitched the yeast yet, you might want to just start with gallons - that way you can experiment a bit with different yeasts, sugar, sgs etc.
As far as getting close to a JK Scrumpy - thats a tough one. Here's a thread on doing a clone
https://www.homebrewtalk.com/f32/anyone-sucessfully-done-jk-scrumpys-clone-125852/
JKS is not easily replicated. Its a natural ferment done at lager temps with a great apple mix (Northern Spy, Cortland and Jonathan) that has been intentionally nitrogen limited and probably sweated to increase sugar content. SG is 1.024 but it doesnt taste all that sweet because the flavor from the natural yeast is so intense that it balances the sugar.
The closest I've had to a JKS was made by the guy who runs the cider mill I use. He used unpasteurized Stayman juice and left it in a 50 gallon barrel in an unheated shed over the winter.
I've had mixed results with natural ferments. I've had some really good ones, but they are a lot of work to keep stable and then crash unless you have a lagering setup. At this point, I've pretty much made up my mind only to do gallon batches for natural ferments from now on, because doing keg batches is so much work. Besides which, I only have a handful of friends who really appreciate a natural ferment. For most folks, a keg of S04, US05, Notty or 3068 really hits the spot, and these are much, much less work.
If you can get good unpasteurized juice, then I'd recommend experimenting around with some ale and wheat yeasts to see what you like. Dont add campden because the natural yeast is what gives JKS and similar farmhouse ciders the distinctive taste.
Wheat yeasts are probably the best for getting the wild flavor because they ferment so slow that the wild yeast leaves a pretty good imprint before the cultured yeast takes over. And the cultured yeast is a lot easier to crash, so you sort of get the best of both worlds. 3068 is more like a Normandy cider. JKS is a little heaver tasting, and I would say the heaviest tasting of the wheat yeasts is the WLP380, bumped up with a little sugar.
Personally, I like something a little lighter - for all the authenticity of a JKS or Normandy cider, its hard to beat S04 crashed at about 1.010 or so. You cant crash the ale yeasts too high though. Above 1.012 or so, they get a sort of sticky sweet taste. Wheat and natural yeasts you can crash at 1.020 or even 1.030 without them tasting overly sticky