IDK. If I had a bazillion dollars, I doubt I'd bother with all of that, I'd either hire someone else to deal with it, or live off the interest.
Ok, I have similar requirements so perhaps I can help you out a bit here. First of all, you don't need an investment bank, you need a prime broker who specifically caters to high volume clients. You need connectivity, fast infrastructure and manual risk management. There are more than enough houses that cater your needs, it's absolutely not necessary to pay nosebleed fees through and investment bank. Google "prime brokerage options" and you'll find more than enough. I generally advise against trading SPX options in your situation because SPX options are cash settled index options. That means if someone would be willing to take the other side of your trade, there is no direct hedge to this trade aside from warehousing it into some kind of dispersion portfolio or take the futures market. The edge loss you will face is gonna be huge. A 100k order is nothing to sneeze at, especially in wings. Usually you have to minimize market impact by a time/vol slicer and build your position over multiple days. Trade ES options instead if you have to, because they are a bit closer to equity options when it comes to execution. Aside from that I'd really question myself if I were you. You said you just sold your company and are into trading only since 2019. Size like that is usually done by very sophisticated players. Not gonna lie, I would love to take the other side of your trades, since what you are trying to do screems "Dentist" (a truckload of cash but no clue). Anyways, just my 2cts. I'm doing this for a living, so perhaps not too many grains of salt necessary. For further questions better PM me. Most of ET has no idea.
I am in a similar position with a fairly large account from a liquidity event, but I trade single name equities and options. TBH I spent a lot of time looking for a semi-pro offering (sometimes confused with mini-prime) and have met/spoken with many. Nothing beats IBKR for an armchair individual trader I found, regardless of account size. It takes time to get filled and a lot of order manipulation in my case but that is not a bad thing I found. Speed of execution does not always correlate with returns.
Yes and no. I use Excel formulas to determine size, price etc...and send via API. Pretty basic stuff.
And p.s. many small and mid size hedge funds use IBKR prime as well. Praetorian comes to mind. Probably the best lesson I learned from ET was someone who said a few years ago: if the problem with your strategy is your broker, it is your strategy that needs reviewing. I have learned to make the best out of IBKR to avoid wasting time and energy on a complex EMS/OMS/Custody setup.
"if the problem with your strategy is your broker," that means switching broker will make your strategy work better. If switching broker can not make your strategy work better, then your problem with your strategy is not your broker.