This is a really good question. If you are a beginner trader, I would recommend that you only Buy when the day chart and 4 hour chart (according to your example) BOTH indicate a buy signal.
This serves two purposes:
2) Such situations take time to develop, and this is a great way to train your trading discipline.
This being said, if the day chart says 'Buy' and the 4 hour chart says 'Sell', you may also enter a Sell trade. However, this is generally only recommended for traders who know exactly what they are doing. This would be a higher risk trade, and once your profit target is hit, you must quickly exit that trade because prices are likely to soon turn against you.
What is a good stop loss number that you use?
My answer is: It depends. I don't use a fixed stop loss.
Most of the time, my stop loss allowance depends on the prevailing volatility in the market.
For example, before the credit crisis, a stop loss of 20 pips for the EUR/USD pair may have been perfectly reasonable. When the crisis hit however, with the increase in the average trading range, a stop loss of 20 pips would be hit far too easily, especially if you are a beginner trader. (Note: I'm referring to trend trading here; not scalping)
In such a situation, I would typically increase my stop loss levels to cater for the increased volatility.
Should I use a or ?
If you are a beginner trader, market orders would do just fine.
As you gain more experience and start becoming more profitable, you can then start using limit orders to enter into positions with greater accuracy, profits and lower risk.