1. Make sure wood is dry enough to work with. Wood needs to be around a 7.0-8.0
2. Make sure wood is straight and not damaged. (Dry rotted, etc.)
3. Use the wood just like I would if it were from Lowe's
I guess my question(s) would be, do I need to plane the wood? Do I need to clean it or anything or does the planning do that? I don't own a planer, so what are my other options?
I just return from a project down south helping a friend on a "barn to home conversion." These structure dated from the late 1700's to the early 1800's. Vintage wood, historic conservation/restoration/replication is a larger corner stone of my professional work. I will try address you query (and any others) the best I can when able (traveling at the moment back up north.)
No, wood does not have to be dry at all, not that this would most likely be an issues for vintage barn wood.
This is a very modern and often over spoken disjointed view of modern wood machinists and there approach to wood working. Wood, the majority of it through history actually, was worked green for the brunt of the majority of day to day wood items...Including the architecture built with it...as it still is today in many wood cultures, and almost all from second and third world wood cultures.
Even wood that has some degradation can be utilized. I have had a few threshing floors and planking made of maple out of old barns that had been subject to conditions at the end of the barn life that had overtly high moisture. As such, spalting fungus (present in many of the genus Acer ) activated and softened the wood to a high degree in many board feet. Some of this was actually spongy to the touch, yet also had the most active (and attractive) spalting. Wood solidifies and other methods both traditional and modern rendered almost all BF employable. Several table tops, cabinet panels and chairs came out of that allotment.
Curved piece too can be made of good use depending on application, skills sets and design.
I can not really speak to this well...I use almost exclusively green wood from our own or known sawyers, and/or wood that is vintage by nature.
As others have wisely suggested, a metal detector can often be put to good use...or...be prepared to work the wood down with hand tools with quality metal that can take the punishment.
I usually use a Smoothing and/or Scrub Plane in concert with each other to get this work done. Both with rondel edges on the iron ground to 25 degrees and micro bevel of 30 degrees. Planing directly through the nails and other smaller metal items leaving only the large and more visible metal artifacts to be dealt with. This can leaves very interesting contrasts of small metal flecks in the wood.
A wire brush head, or something like a Makita Brush Sander can also help, yet can also raise grain fast...which can be both a good or bad thing depending on design goals.
Without knowing our style of woodworking, design styles, and tooling modalities its difficult to give more assistance of worth...