1. Take the most reasonable amount. There's a custom indi called Spread Limiter or something similar, you can use it to prevent high spread trading as it inevitably will cost you the results. Even better is to use time limits and trade from Sidney open to NY close.

2. Certainly use your broker's data. Save it from your broker's terminal (Save As -> FSB's data folder). You can introduce yourself to other options as well -> https://forexsb.com/wiki/fsbpro_guide/history_center

3. My opinion is that testing a strategy twice does not improve its abilities and future profitability. Secondly, some strats will never show similar results because of MT's bugs in its backtester. Usually they match but it is a fiddle to have correct settings and starting points and so on and so forth, it is a waste of time. Therefore the most vital thing a trader must do is to verify that his/her strategy behaves similarly in a live trading environment compared to a backtest. That is one must compare live trading signals to a following backtest on the same data set.

4. You will not have 100% exactness in profits due to spread variation, slippage, broker tricks etc. It is the trading signal matches which bear the importance.

5. The failure rate can be 10-90%, depends on many factors. There are a lot of books on this subject and web resources, a whole science.

6. For Pro visit -> https://forexsb.com/forum/forum/64/portfolio-maker/

The use of indis is the same, just Studio uses native mql indis mostly. Secondly Studio is browser based, it is more simplified than Pro and therefore a lot faster. Thirdly its capabilities and the scope of use is somewhat larger, especially considering portfolio testing and trading. So if a user is into data mining approach, then Studio is a much better platform to do so.