The Mysterious Relics

Those are raid bosses, I believe, for level 50 content 24-man raids.

You can also buy those items off of Skirmish Vendors (Curiousity, I think), which was the easiest way for me. They're expensive, but worth it.

I'll try and take these on one bullet at a time

• Blitz to maximum level because endgame is where it's at.

No. Take your time. Most of the content is in the leveling. Do the Epic quests for the story. Once you hit endgame, make another character and do different quests to get to the end, since you probably missed at least 60% of the content your first time through.

• Once at maximum level it's all about gear, gear, gear.

Yes, to a small extent. Most people get a bit bored at max level, because there isn't much in the way of horizontal development.

• Instance groups must be 1 tank, 1 healer, 3 dps.

Generally, yes, but LOTRO is fairly flexible. There are 6 slots for a normal instance groups, but many 3-man instances are here and more are coming. It's not unheard of to see 2 tanks and a DPS take on a few of these. Also, there are a few classes that break the mold of the Tank/Heal/DPS trifecta, so combinations can be more creative.

• Professions are relatively useless (in terms of pve/pvp performance) except for the perks at or near maximum skill.

Sadly, yes. Cook and Scholar are two notable exceptions, since they can make popular consumables. Other than that, quest gear is usually much better.

• Get every achievement possible (is there a LOTRO equivalent to achievements?)

In LOTRO, there are Deeds. Hundreds! (Thousands?) Some examples include: Getting the highest reputation possible with all elf factions, killing 240 lava worms, or finding the bottom of a well the "hard way." It would take you quite a while to complete all them, but it seems like completionists have fun with it.

• etc... feel free to add your own and provide how LOTRO is different

For the most part, PvP and Endgame are weak in LOTRO. This is more than made up for by the depth of the story in quests, especially the Epic Quest line. If you're a die-hard-endgamer, there are still raids and such available, but it's not quite the hardcore community that WoW is.