Along with everyone else, I do think this is a pretty-well done post, however I do disagree with your suggestions. The first...just opens up too much opportunity for cheating, or if you let only select people, for people calling favoritism. Second, main problem is that you'd be asking for the Imms to devote time to checking up one the 50 or so people you have playing at any time, and watching them, etc. However, I do have a few suggestions on things to do. Since you mention roleplay, I'll stick to that, and not bother with any of the pk side.

Firstly, roleplay is all about just that. Being able to play some role. To do it well, work on developing your character as much as possible, so you'd know how to react as the character would. As some others have suggested, don't do anything extravagant...roleplay isn't nessecarily trying to be a fire giant who thinks he's a gnome. One of my best characters, was more or less me playing a character as *I* would act in-game. Why? It made it very easy to act as the character would. Even some of the Imms have mentioned about the lack sometimes of people playing a stereotypical storm paladin or such *WELL*. So, specifics of your char aren't the biggest, but having a good grasp on the generals of it. Courageous? Cowardly? Timid? Arrogant? Etc.

Secondly, while it's obviously possible to roleplay by yourself, usually it's more fun with others. With that vein, cabals are usually very helpful to get involved in roleplay. They have well-defined goals, and things to accomplish. (Similar to your D&D quests, kinda) Acolytes are a very good beginner cabal, Heralds tend to be very RP-oriented, but it throws you in the pot quick. Tribunal can be suitable, and personally I like BattleRagers, though they throw you into the PK arena pretty hard. Empire works sometimes, but they'll throw you out quick if you don't do well, and the donations might be hard if you don't know your way around. Outlanders you need to divorce yourself from cities and such, so that could be a little hard, and Scions tend to be a little harder as well, being a mysterious group and things, so harder to get into.

Suggestions of empowerment classes might work also, though yes, definately a goodly god, or a benevolent neutral Imm, and you'll definately NOT want to do paladins. More strict requirements. However, if you go this way, expect a lot of time that you'll be praying, and maybe not be able to catch your Immortal to interact with. Also, though they're somewhat stagnant now, the thief guild in galadon sometimes has some decent roleplay.

Many of these groups, already have something of a mentor-ish relationship. Most cabals, if they're non-evil-aligned, will have members willing to teach younger ones the ropes. Also, the benevolent gods tend to be willing to help teach some. Also, one thing you can always do, is as you said...good rpers tend to end up in the hero-ranks. Just strike up a conversation with those characters. Ask them some of their history, why they joined their guild, etc. A good character will have a past, etc. Some characters might be busy at the time, but some you might be able to talk to. Just that, should probably give you a lot of insight. (Galadon, of course, is always a good place to find people who likely aren't doing as much).

Well...if I think of anything else, I'll come back and add on, but for now, good luck!