I recommend, before cutting any holes, talk to people that do this for a living, use inspectipedia on the web,etc. You most certainly can vent a pellet stove under that wide open porch, just the same as you could a direct vent gas heater. The only issue would be "ground" protection, as the deck is wood, you would need a bit of non flammable base put down, unless your vent is high enough. Look in any Harman manual online, they have real good diagrams about such. Soot is almost never a problem, unless the stove is not functioning properly, as happens with cheaper stoves, OR, a possibility in your case, if that porch faces in the direction of the prevailing wind, in heating season. That would be the only reason I would not vent there, because if the wind blows straight into that porch, you will even get smells in house every time door is opened.
My big question, why build a nice log cabin/house, then go with a bottom of the line farm store pellet stove?
Anyway, do more research!