Greetings! Great work on your Skeena!
I’m not sure if the seat position will have a noticeable effect on the directional stability, but for comfort, my recommendation would be to start with it as far back as possible and then lengthen the tether if you want to try moving it forward. If you use the stock backrest then you will need to place something behind it or add a back band to move it forward (if you move the seat forward without moving the backrest, it will give you a reclined seating position which is comfortable for drifting, but not efficient for paddling).
You can pack things in front of your feet, for sure. It’s not necessary to have your feet touching the front tubes. If you are paddling hard, using your whole body, sometimes it is nice to have something to push off of.
I suggest that everyone should experiment with different paddling positions and postures to figure out what feels good for you in the type of paddling you enjoy.
In case anyone is interested, here’s a detailed post I wrote about directional stability.