@Stephen-I would definitely agree with Petko that you were very heavy on EUR with those strategies. It’s very similar to what Haliffa was trying to warn me about. I only trade with 3 pairs that have GBP in them. I use this as my rule when looking at currencies to trade. For every currency I trade, it is only used 3 times max. So in your case of using the EUR, I have EUR/USD, EUR/JPY, and EUR/GBP. *There is an exception to this rule and that is JPY. I have EUR/JPY, AUD/JPY, GBP/JPY, and USD/JPY. I did this because I am actually quite fond of the JPY pairs as they don’t really move as much as one would think (well according to the strategies that I generated).
For diversification and you wanting to do 10 EAs on one pair, then I would start with the major pairs (EUR/USD, USD/JPY, GBP/USD, AUD/USD, USD/CAD, USD/CHF, NZD/USD) and pick 3 to work with. Maybe split the 10 EAs up with 5 being on M15 and 5 being on H1 or whatever time frames you like to use.
I noticed that EUR/USD, GBP/USD, and AUD/USD tend to move in the same direction so take pair correlation into account as well. I noticed that USD/JPY moves opposite the afore mentioned pairs. I also noticed that USD/CAD and USD/CHF tend to move the same direction as well. Notice I said direction and not necessarily speed. Movement is in an overall perspective, but not always at the same time.
Once you get the hang of it, you may want to take a look at cross pairs as well. :) Hope this helps.