I'm looking at doing one of those crazy compounding betting runs, betting all of my balance to win tiny amounts, then rinse and repeat until I get to a stage where i'll take some cash out, or lose the lot

At present, I want to do this by laying big odds horses and have a few questions.
Is there a way within Betangel, that at a click of a button, I can enter a lay bet that automatically calculates the stake required, using all of my current balance so I don't have to try and calculate myself.
Second question, if the race goes in place, I presume i'd have to click 'keep all' to hold the bet in the market whilst they are running?
And thirdly, if during the race, the odds never get to my lay bet odds, does that mean that my full balance is returned to me, or do I lose the lot?
Hope this makes sense. Obviously I can't try this in practice mode as I have no balance to use
Thanks very much