Successful brokerage startups are usually options related. Optionsexpress sold for $1billion to Schwab, Thinkorswim sold to TDA for $606m, Tastytrade sold to IG for $1bn. The last two were sold by the same person.
Look at cqg.com and www.TradingView.com websites. They have a list of brokers who work with their software. Cqg bought marketdelta who invented volume profiles.
Interactive brokers friends and family account lets you allocate trades. The IB TWS software has lines on the charts for trading though there are many front ends for IB if you don’t like there software.