I've read some info about factions in forum chat, but snooping around I see not official faction info and how it impacts on game play. If I've missed it, could anyone point me at some links?
http://ryzom.com/forum/showthread.php?t=23992
Speaking of the island, once you leave, can you come back?
No, but newly-created characters will of course start on the island.
Next, I just read the blurb about pack animals in tutorials- they can't transport and they can die when attacked. Does anyone really use these?
Packers are usually either left in stables for stationary storage, or foragers/crafters take them to their favorite digging spots for movable storage. Mounts are good for getting faster to places that aren't near enough to any teleports.
Finally, is there a way to pull up server populations? I'm curious to see how many play.
No; no one knows the population(s). Nevrax doesn't release that info.
When I click in the box that appears in the window, a list of actions appears but none of them are my attacks such as Acid 1 or 2, Cold 1 or 2.
That first box lists "root types." For example, all elemental spells (such as Acid, Cold, and Rot) are of the Atysian Missile type. Healing spells are Celestial Missile. Powers and Auras are self actions like Self Heal and Melee Protection Aura (respectively). Extraction, Prospection, and Care Plan are for foraging (and you can probably guess which actions would be in the them).