1) As I said, I've got Prophecies and Factions, and I plan on working through them in the order they were released. If I do this, is there any benefit to buying Nightfall now, or can I wait until I'm almost done with Factions? I don't plan on creating any new characters until I'm quite far along with my Mesmer.
2) I started my Mesmer in Prophecies, but I would like to continue using him through Factions as well. Is there an option to move your character back and forth through the expansions and, if so, can I do the story missions in the upcoming campaigns with a character created in a previous one?
3) Looking at the titles I've currently gained points for, I understand the exploration one, but I don't understand what the "Perfect" requirement for the Tyria story missions means. Does this simply require that you do the Bonus as well as the normal objectives, or is there more to it?
4) I've found several purple items through my adventures up to Nolani Academy (where I'm at now), but I'm unsure as to whether people will use them. From looking around in Ascalon City, it seems people are always selling better items than I've got. Is it worth it trying to sell these low end items to low level characters, or should I just try to salvage materials and such from them?
5) Though I'm admittedly far off from the 15k armor sets, I'd like to eventually get the 15k Kurzick armor for my Mesmer. I've looked around this site and searched Google, but I've been unable to find a list of materials for this armor set. If anyone could share a source that would give me this information, I'd greatly appreciate it.
6) Though I'm having fun working through the quests and story missions, I often find myself having to rely on the Henchmen, since noone seems to want to party. Has anyone else experienced this problem with the Prophecies campaign and, if so, is it simply due to the fact that it's been out so long that most people have moved on to Factions and Nightfall?
Thanks to anyone who takes the time to answer these for me.

I'm now up to Borlis Pass, and it seems there are a LOT more people around in towns now. Whereas Piken and Fort Ranik were practically deserted, Yak's Bend is so full I can barely click on NPCs. I did find some good groups today, so I'm quite happy.
The only Elementalist spells I use currently are Firestorm (for an AoE), Glyph of Lesser Energy (2 energy free spellcasts) and the one that heals you for a percentage of the mana cost of a spell you cast (can't remember the name). Most of my energy problems stem from tab targetting and spamming the crap out of Empathy (on melee mobs) and Conjure Phantasm. When I need to cast Backfire or Firestorm on a large group, I try to use the Glyph of Lesser Energy to make it more energy efficient.