I played FF11 for a couple of years, off and on, so I think I can answer some of your questions when compared to that experience.
1) Very very very easy to play and advance on a casual basis. Experience is easy to get by completing quests, and the level cap is relatively low; level 20. But there are a LOT of skills to get, and you'll spend some money on weapons and armor (but not nearly as much as other games; only for prestige items). Most missions take <20 minutes to complete. Some quests can take longer, depending, but a lot are easy and help you explore the game and find new towns and missions.
2) Player base: depends on the campaign. Factions is pretty paltry, and I'd steer you away from that. The original campaign, Prophecies, is probably your best bet for an active base, with Nightfall close behind. Weekends are, of course, the peak time for any of the campaigns. And PVP is super-active all the time.
3) Headset/microphone depends on if you want to PVP or not. If you don't have any interest off the bat.. no worries. Later, if you decide to join a guild and do a lot of team PVP, it'd be a good investment (a servicable mic shouldn't cost you more than $10-$15 USD) so you can run ventrilo or teamspeak and strategise in real-time.
And your one-shop-stop for all game information once you're playing should be
http://gw.gamewikis.org ;D
So, onto FF11 comparisons..
First, travel is dead-easy. At any time you can press M and bring up a world map, and click on any town or outpost (and there are lots of them) you've been to before and be instantly warped there. No long running times or waiting for airships, et cetera.
Everyone can resurrect. Non-monks generally carry a special one-use skill that recharges any time you defeat a boss, so having a monk die in some random field battle isn't the end of the world, and not everyone needs to sub a "healer" job just to be able to do that.
GW uses something sorta-similar to FF11 jobs, and calls them professions; your primary job can't be changed, but you pick one secondary job at character creation and then later get the chance to unlock the rest of them, and can switch whenever you're not in an exploration (monster) zone or mission.
Ahh.. what else. From the first city you have access to NPC henchmen you can add to your party, including a monk/healer. So you'll never be stuck in a town waiting for "just the right party member", you can always get an NPC to fill for you. And they're actually pretty competant. I've run most of the missions in all three campaigns with these henchmen in one form or another. "Soloing" the PVE content is very possible, and there's even a special kind of PVP battle now just using a special kind of henchman.
Summary: GW's meant to be casual, pick-up-and-play-and-then-do-something-else-with-your-day; it's only a timesink if you really feel like it.