The way you have it drawn there is great, that would be my preference. I understand that won't work with your current dimensions though. Frankly, you can be pretty cavalier with the system if you aren't going to have any mass. You will have a much warmer exhaust then you would if you had mass, so you can get away with some fudging dimensions if you put a bit of a stack on it and use that to pull. I think you might be able to do a basic side connection if it's going right into a vertical stack. It should pull through the pinch. Maybe.
The idea of turbulence is to help mixing of the oxygen and fuel gasses, so it's only useful in exactly the right spots. Everywhere else, low friction is desired, just as you suspected. In a normal system I don't think turbulence in the riser is a good thing, although I've not seen it in many heating J tubes. It does seem to help in cooking L stoves where the fuel is right at the bottom of the riser, so there is no horizontal component to the burn. I think a misunderstanding of the difference in the two stove shapes has probably led to well intentioned riser turbulence inducers. Maybe.
Or, maybe you could do your design with a small intermediary box that encompasses both riser base and exhaust hole, and reduces to bell size on top.