When you are using a tool like a risk management calculator or something similar with the desired output, it gets easier for you to determine the best lot size based on your current trading account assets. Whether you are on your demo account or trading live, you will get to understand the amount you would like to risk.
You seem to have a big heart! I have not personally done it but have monitored a friend’s account who was using an EA that would routinely place market orders of 100 lots or more. Frankly speaking, it was fun and terrifying to watch at the same time.
I am not sure how much you are risking per trade. In order to determine the right lot size, you will be required to determine your risk in percentage. Talking about my previous trades with turnkeyforex and fxtm, I follow the 1% rule. In case a trade closes out for a loss, no more than 1% of my account balance is at risk.