I'd like to start a toon I can tank on. Is warrior tanking fun in Rift? How difficult is it in comparison to any of the tank specs in World of Warcraft? I really only ask that so I can get an idea of the kind of learning curve I'm in for, as WoW tanking on the classes I've done it on (Pally back in Wrath, and Druid and DK in Cata) are really quite easy.
Tanking is fairly easy as a warrior, though wait til L18 til you start, that is when you start getting your first aggro bonuses, taunts and damage reducing talents so it will be a lot easier. Probably the most confusing aspect will be how to spec, but there are guides to help with that.
Are clerics at all desired in a DPS role (dungeons or raids), or would I most be asked to heal as they don't really bring the kind of numbers people want to see?
In dungeons because you spend more time on trash than on bosses and Clerics have decent AoE a DPS cleric is desirable. However in raids they have the lowest single target DPS right now, and are preferable as tanks, healers or as DPS/healer hybrids that support the raid.
Are chloromancer mages a primary/tank healer or more of a support/raid healer? I like the idea of healing by doing damage, but I'm really kind of curious with how the spec handles in high level dungeons and raids.
Chloro can both tank heal and raid heal very effectively. Generally clerics will tank heal because of their pre-shielding abilities and their defensive cooldowns, though a Chloro may be assigned as they do give constant healing which may be desirable in certain environments. In raid healing they are generally the best, though their effectiveness goes down the more Chloros there are. Every raid should have at least one Chloromancer for Radiant Spores (16% (26% with armor bonuses) chance to heal yourself for the damage you just dealt). Mage also have great single target damage, though they also have the most complex rotations to boot.
As far as addons are concerned, do people make ready-made UI's like some people do for WoW? I've seen some really intuitive looking set-ups on some videos. With the in-game UI customization if makes me wonder if such addons are as common or necessary though.
There are far less UI customisations than in WoW, this is primarily because if someone reskins the character and target bars, there is no right click or left click context. The addon API is far less robust/developed than WoWs at this time, but it is coming along nicely. There are some great addons being developed however, there is a raiding mod with alerts, various cast bars, ability/DoT timers, cooldown trackers, a power auras type addon, damage meters, and so on.
Also the basic UI is very customisable, you can literally move and resize anything and there are a great many inbuilt features.
As you can probably tell, I have some basic info on the game (I was watching it when it was nearing release), but am still mostly noob-ish about it. Thanks for any advice.