Regarding rankings, there is one thing I would caution against and that is becoming elitist. There was/is an arena forum on the star wars site where I got my start, and what ended up happening once the rankings got higher for the really good fighters and the average fighters began to lag behind was that elitism began to set in. The top-tier fighters hung out in their untouchable castle and the rest just dwindled off until there was no one else left to fight and the entire arena died. I'm not saying that there shouldn't be a ranking system (on the contrary, I think it could be a lot of fun), but there also needs to be an attitude of "if you're not that great, we'll help you get better" to accompany it. Otherwise the average fighters are left floundering with no guidance regarding how they can improve and they eventually lose interest and leave, and the arena dies. A little positive constructive criticism can go a long way.

Regarding points, I like the 100 for a win, 50 for a draw, 25 for a loss idea, and when it comes to tournaments I vote for a bonus of 100 per victory for first place, 50 per victory for second place, and 25 per victory for third place, in addition to the normal point gain. It gives a good incentive for trying to win, while also preventing the winner from becoming borderline untouchable in the rankings.

Edit: I'm also not saying that there's a lack of constructive criticism around here, as I've seen several threads dedicated to training purposes, but just wanted to reinforce that such things are likely going to be necessary in order to keep this arena community alive as well as help it grow. As was mentioned by others, this community has always been very good at keeping things low-stress and openly inviting. :)

PS: If there is a third place prize, I just realized it would have to be shared by whichever two fighters didn't win the two second-to-last fights, so either they each get 25 extra points per victory, or we just do first and second place bonuses.