The way to go about it would be something along these lines.

First, you want to collect your 25-100 points to complete the wager, depending on the risk you selected. Each index you turn in will add 10 seconds to the timer. You wanna make sure you don't run out of time, otherwise you lose.

Side note:

While each index you turn in will add 10 seconds to the timer. the bonus index you get for holding onto increasingly higher number of indexes before turn in DO NOT count. Therefore, the optimal way to do it would be to turn in large amounts of indexes at once, to minimise the time added to the clock.

Now that you have your wager completed, you will probably have a lot of extra time on the clock.

What you wanna do next, is head to the enemy base and do whatever you can to help the enemy kill you. Each time the enemy scores and index, the timer will reduce by 10 seconds. "Feed" as many kills to the enemy as possible, to finish the match as quickly as possible.

Side note 2:

Bring a self damaging weapon, like the Stug, so you can keep yourself near death, to make it easier for the enemy to kill you and score.

Regarding team composition, the norm goes something like this

Team Info

You want to have a carrier usually, because it is a lot easier to manage and gather large amounts of indexes, to take advantage of the turn-in bonuses, if you are not competing with your teammates.

You want to have a high damage dealer. The faster the enemy dies, the faster you collect indexes. Mesa is usually picked cause she can aimbot across half the map

If you want safety (can be useful for high risk, med and below not really needed), then pick up something like a slow nova. Lvl 100 slow ass enemies are not quite as dangerous.

If the other teammates cannot be bothered to collect energy orbs, then a trinity can be deployed. Useful if you want to just focus 100 on your task and nothing else.

Hope that helps.