TradeStation offers a complex platform for active advanced traders who want to design and test custom trading strategies. Just a guess but I have a gut feeling that is not what you need at this point.
I think that your priority should be a broker that offers the lowest commissions for your frequency and size of trading/investing.
If you trade larger blocks of shares, you'd be better off at a fixed fee broker like Ally, Fidelity or Schwab ($4.95 or so per trade).
Merrill Edge charges $6.95 per trade but if you maintain a combined balance $50,000 with them and parent company Bank of America, you're eligible for 30 free trades per month ($100,000 gets you up to 100 free trades per month).
If you want to scale in and out of positions, Interactive Brokers charges a 50 cent commission per 100 shares ($1 minimum charge per trade). Newer broker tastyworks has competitive commissions but isn't as sophisticated as IBKR, yet.
Your secondary considerations should be based on what your other needs are. Does the broker offer good research? Good charting? Good option analytics? Low margin rates? Portfolio margin? Trading algos for placing more complex buy/sell orders.? Real time news? Is the trading platform reliable and easy to learn? Is the broker effective at obtaining borrowable shares for shorting? Is customer support good?
It's sensible to have two brokerage accounts because one broker's server could be down and you would have no way to defend your positions, if necessary. As for your possible need for two brokers because you might accidentally close long term positions when inclined to only close trading positions well, if that's a concern then you are definitely not ready to day trade. With day trading, you have to be cool as a cucumber when it hits the fan. You have to be able to separate the emotion and be able to think clearly and not become the deer in the headlights. I'd suggest that you trade small until you get some experience and avoid margin trading until you have a lot of experience and can function under pressure.