The Jet 1015 is an awesome choice. If it's made anywhere close to the quality of the older Jet1014 then you'll have a piece of equipment that will wade through the fire and come forth shining as gold. They're tough, solid machines.
As far as chucks go, Novas are great too...as it seems you're already aware. That said, I would most definitely go with a fixed thread.
1x8 tpi threads are really common on most machines of that class and the accessories for these in that thread pitch are readily available.
Now then, although I own a Nova chuck and really appreciate their brute strength and functionality, if I was going to suggest a chuck I'd say take a hard stare towards the Easy Wood Tools brand 'Easy Chuck'. No more stripped screws and attempting to locate replacements. Easy Chuck--jaws off and swapped in less than 10 seconds..tops!
You don't necessarily even need a chuck to make duck calls.
Mandrels--there are only a few options in that realm. One would be better striding that road and marching along the beats of making mandrels as opposed to game calls. There are tons of us making game calls but hardly anyone making mandrels. The profit margin is just sitting there awaiting like low hanging fruit. Just a little digging...you'll find.
The Jet1015 will be fitted with a morse taper (MT2) in the headstock therefore any tapered holding jig / mandrel you buy would need to be a MT2. Now then, lots of callmakers elect to use the straight shafted mandrels and not tapered, in consolidation with a collect holder. Much easier removal and quicker dismantle.
Drill bits--you'll need standard twist bits and brad point bits. Brad points are absolutely essential. For drilling larger holes in this realm of callmaking--source some 'twin land' bits. Don't go cheap on bits. In the department of bits, metallurgically you get what you pay for. You'll reap huge returns by just spending that extra $10