1. The watch looks fine on his wrist and black dial would be more suitable for a formal occasion.
2.This piece is rare mainly because of the number produced but the movement as many have said is quite common unlike some of the other limited editions. It remains one of the least desirable limited editions of recent times and this is indicated by the used prices.
3. Of all the Pagodas, I actually like the R best as it appears the most elegant of the 4 metals But that is purely my opinion. The height of the case makes this watch not the most practical for daily wear so unless one is very careful, I would not advise it. Yes the P would be harder to scratch than the gold models but still, the watch should be protected by a force field to avoid a close encounter of any type! 
4. The P would hold its value primarily due to its rarity (especially if your friend is buying it at a good price).
5. As Francis mentioned the 5100 series with the 10 day power reserve should definitely be considered or even the 3969R (450 pieces) jump hour for the 150th anniversary. The latter in particular I believe will be a good investment as Patek seldom make jump hour watches apart for the 150th and 175th anniversary. And prices to me are terribly undervalued probably due to the size of the case.