that is personal choice…basically this depends on the following:
1. How much money you will have in your account
2. How many EAs you are going to place there
3. How much risk in total your EAs could bring in one moment
4. What is your money management?
You need to have a good balance between these things, because if you use small margin and in the same time you place many EAs it wont work. As well if you have a small account with many EAs, as well it might be a problem.
The best thing is place on Demo(size as planned) the number of EAs that you want to trade, and you will see in few weeks times if all is good, or what you need to change.