The design tenets for FBAO are:
No grinding - the players should always have something interesting to do. There should be no reason to do the same thing a hundred times in a row. Skills will grow when you put points into them, not by using them. If you decide to climb the same cliff 100 times in a row, you'll still have the same chance of falling next time. If it's not fun, you shouldn't have to do it.
Reversibility - There should be very few immediately permanent decisions. If you're putting in your skill points, and click on the wrong skill, the game shouldn't screw you over (or demand real cash to change it). If you want to put a point into Climb, just to see what you can get to, that shouldn't be to the detriment of everything else your character can do.
(and, more when I come up with them)
Now, let's define some terms. There's a lot of similar games that use different terms for the same things.
Firstly, we call them "characters". "Toons" is not an appropriate term, for obvious reasons, and "avatar" is too highbrow.
A "channel" is a separate copy of the world. There are, say, ten different channels. If the Big Fire Pit is crowded on channel 2, you can just go to the Big Fire Pit on any other channel. It'll have the same stuff (and hopefully be a bit less crowded). Apart from the players on them, they're identical, and you can switch between them any time you're not fighting.
Could different channels have different rules? I can't see a good reason to. If you can switch from PvP channels to non-PvP channels and do hit-and-run attacks.
Each characters has a primary set of skills, such as fighter, priest, or dancer. This is called a "class". (I know some games call them "jobs", and the idea of calling the secondary classes "part-time jobs" appeals to me, but...)
A "guild" is a large group of players (5-100). It's permanent (or at least until you leave or get kicked out). I'm not planning on there being any mechanical benefits for being in a guild.
A "party" is an impromptu group of characters (2-10). Many beneficial spells affect all party members. If one character kills a monster, all party members in the area get a share of the experience points. Party membership might only last for as long as you're logged on, then you have to rejoin (or find another party).
Is there a difference between a party and a brood? Originally, we called them broods because we wanted to be different. Then we stopped. If we decided to be entirely accurate to the way the game was in the comics, a brood would be larger than a party, but smaller than a guild. Or maybe smaller than either (and we'd adjust the minimum size of a party).
I think that's everything. Next: