Kelly formula works for bets with even outcomes like coin tossing which is typically not the case in trading - as you say. Therefore calculating a Kelly % may not tell you a lot. You can read Ralph Vince's book "The Leverage Space Trading Model" on the topic if you want to dig deeper.
Correct. You need to open a ticket via account management / messages and request the change. Then you will receive the forms which you need to fill in and sign as I posted earlier.
You don't pay more for market data, certainly not at IB. The classification for non-professional status or professional status for market data is completely different from the qualification as professional status for PRIIP and MIFID purposes.
Maybe this helps:
https://marcuardheritage.com/wp-content/uploads/2014/06/4_20130801_MCL_Client-Categories-and-their-differences-in-protection.pdf
My personal take on this whole client classification issue is as follows: if you ever want to be in a position to held your broker or bank harmless...
I opened a ticket at IB and requested to be qualified as professional client. After a couple of days I received two forms which I needed to sign and fill in.
In order to be qualified as professional client you need to satisfy 2 out of the following 3 criteria: a) equity account of min. €50k +...