The latest version of EA code is optimized for using lower number of bars. However, some indicators that use Exponential MAs need more bar. The EA loads as many bars as necessary in order to make the indicator value stable. The loaded bars from an EA may reach to 3000 in such cases.
Therefore, the resources needed depend on the number of EAs and the number and the type of the indicators used.
There are two main dangers when using a greater number of EAs (lets say, more than 10):
- Lag in execution - the EAs execute orders synchronously. That means. if an EA sends an order, the other EAs are waiting until the first EA receives a respond form the server. When the first order is completed, the next EA with an order will proceed. If it happens that several EAs trade on one price (lats say Bar Opening), the execution of multiple orders may delay.
- EA interference - It is possible (in rare circumstances) an order form one EA to be seen and modified (closed...) from another EA trading on the same chart. I'm not sure when it happens but it was reported in the forum from at least one user.
I have no personal experience with trading more than 12 experts, so I think other users may give a more relevant respond.
Please study your system well before starting a real trade.