I need to replace the posts on my porch and it looks like doing this
will be the best way to go about getting the job done.

I don't need much in the way of supporting strength, as the porch is
small (8' by 13' and 8' tall), and I'll be replacing 2 "3 S" corner
posts with 3 of these wood columns.

I'm currently considering using bald cypress (Taxodium distichum)
because I can get it straight from the lumber yard. They have 6x6
posts, but they're green, and otherwise have a decent selection of
kiln dried boards. If I select carefully, would buying the 6x6 posts
be a good option, or would it be better to buy some of the smaller
boards and build up a column out of those with glue and nails? If the
latter, what's the best way to combine the smaller boards to form a
square column?

Thanks,
-Nathan