What needs to be considered when building a system?

I'm in the process of building a system I have an idea for. I want to have all my bases covered. What are the considerations I need to have when developing a system? So far I have:

1. Money Management which includes trade size, and TP/SL ratio
2. Entry rules.
3. Exit Rules.
4. Which currencies to play.
5. What time frames to play it.
6. What to do around news and/or are there certain times to not place trades no matter if a signal is made?

What else is involved in a system that I need to build?

Thanks,
Matt

Robustness:

Basically, something which works in as many market scenarios as possible. To my knowledge, there are three main scenarios.

1. Market moves up
2. Market moves down
3. Market moves sideways

If your system is profitable in all three, you will be golden.

Personally.....I think that you have too many variables..

Determine the trend...trade the trend and Exit. Everything else just gets in the way.

Well I'm building a scalping system. Does that change your thought?

In response to the original post, in my opinion you have it back to front for some of the aspects of the system, I would decide on things like time frames and symbols based on what showed the most profit potential for a given idea.

Very good point. Sometimes it is easier to build a system around the currency. For me it is building the system I'm comfortable with and then finding the currencies that compliment it the most though.

I thought of another factor that might want to be considered: re-entry.

I think you have all the variables... maybe also... some time rules.. ofr example.. if the system is traded on friday afternoons.. or sundays... which usually is not a good idea.

Is it a Manual system or Automated that will help determine what you may need to take into account.

Automated. I haven't built it yet, but it's going to be a quick scalping system that I would never be able to do manually.

Have a look around this

http://www.forexhit.com/

it's a big site with a lot to get you thinking about.

This is a good start one more thing I would suggest is a trading journal.