Play Set Staining Help

Hello, I have a play set that I built using reclaimed barn wood that needs a new coat of stain. Also, around the playset I have a border that I used treated rough sawn southern yellow pine 5x5's for, these should be plenty ready for a first coat of stain as well.

A. The previous stain was applied 2 years ago (barn wood only), about when the wood started seeing daylight.                  Before that the wood was inside a barn built in the 1890's.

B. Most of the wood is rough and not sanded, this includes some decay and bug damage. 

C. I assume the old stain needs stripped and I should use a wood cleaner or brightener? I would like to remove the UV damage to bring back some color, such as using the Armstrong Clark.

D. Best application method? Brush, pump sprayer, airless sprayer?

• 1. Indiana

• 2. Full Sun

• 3. Unsure, whichever hardwoods were cut down nearby to build the barn

• 4. North side, which is the rock wall seems to be the only area with mold/mildew

• 5. Previously used Sherwin Williams super deck oil based transparent stain (6511-52639). While it looked great at first it did not provide protection for much longer than 6-12 months and weathering/discoloring started to appear, so now a lot of the wood looks gray/white.