To answer to your $20000 max lot size question.
100000 opens 1 standard lot size
If you are unleveraged say 1:1 leverage the max u can open is 0.2 theoretically. However you must be an avert trade, perfect entries barely without retrracemets. Calculation 20000/100000.
How ever if you are leveraged you can open much higher. Say 1:100 leverage means you borrow X100 giving you $2M. There fore 2000000/100000 = 20lots.
The higher the leverage the higher the lot size you can alot
However these are mathematical possibilities you will need psychological edge in being a perfect trader. With this mathematics you can wipe out your account in even less than a min!
A lot must be considered in selecting a lot size such as margin stop out slippage spread devil’s spikes etc. This won’t work for you especially if you are swing trader because you have to give allowance to retrracemets and swaps against you. So at the end of the day its so much of risk management money management and absolutely SKILL SETS!!!