I am building a playing swing set with rough cedar, #1 should the "furing" be removed to prevent splinter, #2 would the furing come back as it aged, #3 does it need some kind of sealer to make it last longer (10 years ), #4 do the bottoms need end cap (they will sit directly on dirt)

The answer to all 4 questions is yes

Most yard sets are made with redwood

God luck

Chuck

If your kid is going to swing on it you want it smooth, comes both rough sawn and smooth. The roughness may slightly return with time but you will need to lightly sand and reseal every other year to keep it looking good. Cedar is rot resistant not rot proof so a stain or sealer is advised. Legs can sit directly on the ground but that will be your first rot point. Soak leg tips in a waterproofer like Thompson/s Plus or Advance, better yet place a scraficial pad under the leg.