Stay as a single class Bard, do not multi-class it is not needed.
You will have a good chance to live, because the Bard is the master of unconventional (in D&D) terms warfare.
Max out Charisma, try to have as high of Dex as possible, use your wealth to buy stat boosters of those items.
Racewise I would go with Half Elf.
Skill Focus: Perform and Improved Initiative are musts. You want to go first. Max out UMD, Diplomacy, Bluff. Make sure to get all the possible synergies from 5 ranks in skills like Sense Motive, Bluff, Knowledge Nobility, these will pump your Diplomacy score through the roof.
1st round of combat: Use your Fascinate ability. You may be able to effect all of the other combatants dependent on the arena shape, and wether they make their saving throws. The DC is based off your Perform skill, so make sure you have a Masterwork Instrument to set the DC as high as possible.
Now use your Suggestion, Bard Ability. Something like "attack bob, then billy, but not me". Keep in mind the only limitation to Suggestion is the request has to sound reasonable, and be not obviously harmful. This is where Diplomacy comes in, and 'roll playing'. Dont ask for the moon when using the Suggestion, but since clearly the players on the receiving end are going to say their characters dont find any request as reasonable, ask the DM for an Opposed Diplomacy versus Sense Motive check.
You Diplomacy is going to be sky high.
You will come very near to wining the battle here. Keep in mind anyone who makes the Fascinate saving throw is immune to it for 24 hours. Have those that failed the saving throw attack those that made the saving throw.
Combat Buff wise Rage coupled with the +4 to hit/damage from Inspire Courage & the +2 to hit from Inspire Greatness and the +4 to saving throws and AC from Inspire Heroics, and you should be fine in the Melee department. It will take you a few rounds to get all these up, but Bards can buy themselves time.
You do not even have to resort to melee as the first option. With your maxed out Use Magic Device, have some scrolls of Dominate Monster on hand, make the other fight for you.
I would also learn alot of languages. A cheap tactic is to try to befriend other people's Summoned Monsters. You can use a quick Diplomacy check on NPCs with a minus 10 to the check score. The DC to outright subvert a Summoned Monster assuming you speak it's language will be DC 60.
Assuming you are a Half Elf, with the Negotiator Feat and Skill Focus: Diplomacy, and all the synergies bonuses, you should have around a 40 Diplomacy, so you can make it in one shot if you roll a 20. More than likely you will be spending a round to make it friendly, and then another round to make it helpful.
If you go the controller route, you should win the battle easily, and with style, which is the essence of the Bard.
Monks and Paladins will be tough to control, kill them first.