Ok the only combo you would be able to equip a bow or xbow is Wd/S and D/S not any class combo because you have scout as one of your classes.
Xbow is better damage while Bow has better range...find out by looking at Shot to see the difference in distance between the two weapons.
I believe the dump stat for druids is Stamina, or Wisdom but if I remember wisdom is only needed till around 8k which can pretty much be obtained from plussing your gear and equipment that has wisdom as a ghost stat.
Wardens primary stat is Strength, while Scout Primary stat should be physical attack, Strength and Dexterity grant the scout the same amount of physical attack so you can use dex/pa or str/pa, some even go with str/dex stats.
If you are planning on making scout your primary then s/wd is very solid scout. A bit confused as to what your intentions are for your character thou...you posted in scout forum section so are you planning on playing scout as primary?
Chiron not Charon...the Centaur ( lvl 30 Wd/S Elite Skill ). and for Class combo Elite skills this is not a bad site to look at
http://runesofmagic.gamepedia.com/Warden…arden_.2F_Scout ( may have to copy n paste but is Runes of Magic Wiki Elite Skills section ).
As far as ammunition goes at level 55 you can obtain a bow or crossbow from ZS/DL that lets you summon arrows without having scout as primary just be able to equip the weapon. For Scout Primary there are two Item Set Skills that grant the scout the ability to summon magic arrows but just a heads up all these arrows that are summoned either by the bow or item set skill will vanish once you log out ( this does include getting booted or discond ).
If scout is your secondary then you will have Vampire Arrow and Shot as scout attacks that will be based off your physical attack.
The D/S I am not sure has any physical ranged attack elites, I know it gets healing arrows but ammunition is not required for this skill just like no ammunition is required for vampire arrow just focus ( scout energy ).
The only pointer I can think of is if you plan on having scout as secondary then most people just use the bow slot as a stat stick. So the type of weapon bow or xbow you use really will not make much difference.