> 1. How can I change the backtesting time period?
You can use the Data Horizon tool in Control Panel. You can set the From and To dates for the backtest as well as the maximum number of bars.

> 2.  How come the Pessimistic & Optimistic method have so much difference?
It seams your strategy has many Ambiguous Bars. These are bars for which the backtester doesn't have enough information to produce a single result. We provided several Backtesting methods to deal with ambiguous bars. The default one - Pessimistic interpolates a bar in a way that shows the lowest possible result. Optimistic shows the highest result. Shortest method is is near to the MT backtetsing method. See more info here: Reliable Backtesting, Method Comparator.

> 3. How come I can't back test the EA in my broker's MT4?
MT backtester is super super noneffective and unreliable which was the primary reason for me to develop Forex Strategy Builder. Other reason fort he slow work is that our indicators are not optimized for the MTs way of calculation.

You cannot make anything except to leave it working.

Eventually, you can select a lower time frame (5-15 min) and to limit the backtest for a month. Switch on Visual mode and monitor the entries and exits. You need to see one cycle of entry (adding and reducing, if any) and exit in order to confirm the correct work. If it works for one entry and for one exit, it will work for the whole testing period. You can add also indicators to the MT4 Backtester, if you set the the same parameters, you'll be able to compare indicator values.

You can also connect via the Bridge and to compare indicator values with the exported expert.