We recommend only 1 ea or indicator in only 1 pair for each mt4 / mt5.
more than this will run the risk of mt4 / mt5 hang "not responding".

DO NOT leave all symbols open in the Market Watch. This will eventually build unnecessary data file bigger. During peak trading hours, it will also pull a lot of data traffic and will potentially cause your mt4 to become "not responding". Advise to hide all symbols after done setup trading pairs.