I believe, for the most part, J.S. sources their kits from Pecatonica.
In fact, if you follow this link you will get a "photocopy" of the J.S. listing
(Pecatonica Tulle)
(and if you do decide on the kit I would deal directly with Pecatonica River - that way if there is a problem you can get it solved by the "source" instead of a "middleman")
Given that, you will get a partially shaped stock, ramrod hole bored, barrel channel cut (as far as the breech - breech will need to be inlet).
The lock, trigger guard and butt plate will be about 90% inlet.
Plug you will get a "box of parts" (see the Pecatonica site page).
This kit is not beyond a first time builder, but since you will do some learning along the way I would budget, minimally, 100 hours before she will go "bang".
This is not a "put part A into cutout B" kind of kit - there is fair bit of woodwork, metal finishing, polishing, sanding/scraping, inletting, filing etc.