mcMMO is a Bukkit plugin that already exists. It allows for every player on the server to have stats similar to a true MMO. And the combat areas are: 1)Unarmed (no weapon), 2)Swords, 3)Axes and 4)Bows.
Here is mcMMO in a brief summary (i will post the link to the full wiki page as well):
I am going to use the sword as an example. (There are multiple different stat areas in mcMMO). With the sword, each hit on an enemy, PvE or PvP, adds experience to the player in "Swords" area.
Experience is gained on every SUCCESSFUL hit on an opponent. Example: Zombie hit - 10XP, Creeper Hit-15XP, Enderman hit-20XP, Player hit-25XP etc. There is no bonus, at least in mcMMO but you may want to add it, for a "kill" of an enemy.
After so much experience is gained, the "Swords" level will increase. At every increase of level, there in an increase in damage done with a sword, there is an increased chance of a passive special ability (such as "counter attack" or "parry"-where there is always a random chance that a player will dodge an attack from another when he/she has a sword in hand) and at set levels, the player will unlock an active ability (accessed by right clicking).
Sword example:
Every level up
-increases chance to counter attack by 0.005%
-increases damage by a random value=(Current Sword Level) * Random( 0, .5)
(This may seem weird at first but it just means that there is no chance of added damage at lvl 1, slightly higher chance at lvl 2 and so on)
This value would be increased either on a "per hit" basis or it would be instantly set as a value when the player levels up the stat. That choice would be up to you and i'm not sure how it is currently done.
To read up more on mcMMO:
http://mcmmo.wikia.com/wiki/McMMO_Wiki
Finally, i spent a fair amount of time on a server that had mcMMO installed and already have made basic "training" areas to level up each area so i could easily build multiple of each on your server in the waiting area to make this feasible if you wish to add this functionality. I really love this server idea and have watched multiple of Bebopvox's and ChimneySwifts's gameplay on the current map and would love to help in any way possible. Thank you for your time. And may the odds always be in your favor.