I run a 16x54 ( length doesn't mean as much as width, width is the same). Heres what I have found and had confirmed by some guide friends.
2 strokes weigh less and on a DB that means a lot. 4 strokes are still too heavy. In a couple more years they will have them weighing the same, but for now, stick with the 2 strokes. Go with a 10 horse over the 8. The weight is the same, just different carb and internal stuff. ( Sorry I can't be more technical, I'm not mechanically inclined). You'll be able to get back up to the top of faster moving water with it. My friend has an 8HP and can't make it back up in spots where I can, or at least it takes him forever. Also, your 17 footer weighs a little more and can carry more than most 16 footers, so the extra oomph would be nice.
Oars are dependant on where you fish and personal preference. I fish the upper Rogue where some of the water is technical and quick pivots are needed. 9 foot oars are perfect for this. 9'4" are ok too, but anything longer is too much. Double-check with Mike at Willie for more info, but I believe they normally sell 9 footers with the boat you bought.
Enjoy your boat. Thats the one I'll be getting in a couple more years. They have great responsiveness (probably more than the 16 even), and the more you put in them, the better the row...not too common for a driftboat.
PS... don't forget to rebalance your boat with the motor on. I have to move my front seat up 1-2 notches depending on who is with me.