Tracking is quite easy...
Challenger Player must submit that they are playing a game and who it is against...
When the game is over the Winning player submits that they have won the game.
The stats are up dated..
I love stats... So I could keep track of the stats... What ever stats people would want to see. Such as history vs each player etc...
I have all the software available to do this stuff.
Databases,,, spreadsheets etc...
Updates could be run once a week or month or bi-weekly etc...
What ever people wanted.
On the subject of challanging people below/above you...
If you lose your score would be adjusted per ranking and score.. that way the punishment/benifit is little score increase or a little score decrease..
If a player is currently playing a game they could refuse to play that challenge. That way the player would challenge other players...
As i have seen on other ladders..
Current games could be listed .... so you would know who is playing...
And this system could be used for the two player games as well... That way you know who you played and who is currently open for a game.. who you can challenge...
Or even combine the two
now my head hurts
Either way i like those two systems... I see merits in both of them...
About Game Play
Geo I think Pre-Designed Standard maps would be the way to go.
10 two player maps.... That way there is some variation... and an equal footing on startup.
A couple of Tournment Maps if you wish for 3 or 4 player games...