I agree with the last few posts. It's not only about skills or saying the right thing. It takes a certain personality and/or mentality to become a speculator. Traders are not "normal" people. Even if you have what it takes, you also have to love it and desire it badly, otherwise you won't be able to withstand the work, the psychological and the physical punishment of trading.
I would not approach the interview with "I want to get the job" attitude, rather, let him tell you if you are trader material or not. It's not a job, where you go to the office 9-5 and then forget about it, it will become your life like it or not, it has to, in order to become successful.
Not everyone is succesful, so it's good you have some money to fall back on later if the trader gig doesn't work out well. On the other hand, I think you already have the disadvantage that you are not poor and hungry, so I'd ask first how happy you will be with something as hard and demanding as trading given that you have already some net worth. Then I'd ask about any personal previous trading experience because you already have had plenty of opportunities: some money, exposure to the markets through a software company, I think it's not a good thing you've been waiting all along for someone else to fund your trading or to tell you what to do in order to make money.
In my experience the first guys/girls to abandon trading aren't the least brilliant. It's usually those that get upset because they have sometimes to watch the markets overnight (position traders) or have to forget about lunches and other personal stuff during trading hours (daytraders), or not willing to work on research and other due diligence on nights and weekends. Then it follows those that get impatient about the learning curve, or take losses personally and so on ....
BTW I think you have an excellent background for investment banking, pity this is not the best time for that career.