Hi Harry,
Im sure Petko will confirm but I would expect the only EAs to trade long only to be indices and forex and commodities will be long and short.
The answer to your second question is yes.
Once the EA is removed it is no longer managing any trades that are currently open so you would need to close any open trades from that EA manually if removing the EA. This is easily done by looking at the comment in the open trades in mt4 or 5 terminal.
Last question is a bit subjective but one way to do this would be to trade at least whatever the maximum stagnation period is for the strategy
hope that helps