You need to include in your strategy: entries, exits, and position sizes. It all needs to be based on your own philosophy and your capacity to consistently carry it out.
Time frame: How often can you look at market information and readjust your orders? Can you do so every minute around the clock from the Asian Monday open to the U.S. Friday close? How about every 5 minutes around the clock all week? What about every hour? Every four hours? Are you working a full time job? Going to school? Living your life? How about looking at just daily data and making readjustments once a day? Will that better suit your lifestyle? Or what about once a week? What if you simply readjusted your orders just once a week using weekly data? Would that be more coincident with your schedule? These are the questions that will get you to the time frame you should be looking at. It won't matter that you can make more money on the 4 hour charts than the weekly charts if you simply don't have the time to trade four hour charts.
Besides, the costs of trading smaller time frames are a lot higher than trading longer term. Many of the most successful fund managers in the world therefore trade on daily and/or weekly data. They pay no mind whatsoever to intraday price changes and they make tremendous returns.
Your system is not about what will profit just any trader, it is about what will profit YOU. You need the system to work with your life, with your psychology. If you adopt a system that you cannot keep up with, you will ultimately fall behind.
All pairs are alike. It doesn't matter what pairs you trade. But know this: The fewer currencies you trade the fewer your profit opportunities are and the more consolidated your risks are. Traders specializing in a given currency can go long periods without profit earning moves while they watch other pairs trend beautifully. And traders with all their risk in one pair can be wiped out when that pair goes into convulsions on surprise news while others continue trending beautifully.
My short answer: Give a good strong consideration to long term, diversified, strategies.