Estimated reward is what would you get if a block was found at the very moment. Bare in mind, that below mentioned formula only applies if you mine during the whole round. For more information see score-based reward system.
Unconfirmed reward is a reward for block that was found, but not yet confirmed. Rewards for such block are pending until Bitcoin network gives us 100 confirmations.
Confirmed reward is what you will get. You must however reach your payout threshold before any payout could be made.
For optimal performance keep mining 24/7. See following article to know how to set up mining in Slush's pool.
You can use online calculator to determine how much can be made with your mining hardware. Just insert hash rate of your miner and get your approximate reward.
See the question above and the following article
Your confirmed balance is sent to you once it crosses the Send threshold. For detailed explanation see following article.
Every user receives a reward proportional to his participation in the pool's mining power. If your scoring hash rate is 1% of the whole pool, you receive 1% of the block reward. If you own 0.031% of hash rate, you receive 0.031% of rewards. It is that simple.
If you are interested in deep explanation and the math behind this concept feel free to read following article
All that it comes to is really finding a sweet spot between short payout period or bigger amounts.
That said, you should decide for yourself based on how often you want to get your rewards and the speed at which you are able to mine such amount of BTC.
The minimum value is 1 mBTC. Just keep in mind that additional fee of 0.1 mBTC applies to payouts below 10 mBTC.