I owned my own construction for 13 years. I built several houses with exposed ceilings that was from the decking with T & G. I would recommend Cypress 2x6 T & G rather than 1x6 T & G. The 1x6's don't have enough thermal value. In all the years I built, I only used 1x6 T&G on the decking (at the insistence of the home owner. After one summer, he paid us to come back and rip it off and put the 2x6 T &G. Aspen is the same as Poplar (the other name for Aspen)which is a soft wood that has 0 rot resistence. Cypress, on the other hand, has a world renowned reputation for rot resistence.
Traditionally, Western Red or Aromatic Cedar is used for the posts on porches (either whole trunks or sawn posts).
As to the porch roof, since it is a porch and it will have a metal roof, you can use 1x6 T&G on it without negative effects. It will not be fighting the AC. Hope this all helps.

Keith in Houston