Please explain, rustic meaning it would look like trash? Another way of asking, would pine 2x4's look similar to solid wood pine boards?
Framing lumber will not get you the same asthetic results as grade a or select grade pine will.
If you want a deck like look, just screw em together. If you want a more refined look, you will have to do alot of work planing and jointing the surfaces to get a good clean look. Also you will have to be real picky when choosing the 2x** as the grain structure is very important in this application. 2x** tend to warp and bend at the lumber yard so be aware of that.
Tools are like guns, You can never have enough. Where did I put that tape measure???