Nope. That was probably just to get you to pay more fees for data, now that you are "professional" and all. Sounds fishy to me.
Correct, but be prepared to answer quite a few questions from your broker and sign a letter stating what brocklanders wrote.
There are tax advantages to having a C corp and a personal business. This is one of the main reasons to incorporate in my opinion. There are legal ways to shift income between your corp and personal business to help defer taxes, you can't do this in an LLC though. Also it's easier to have health insurance and some other benefits paid out of the corp. The hardest part is finding a smart aggressive accountant to help form a tax strategy so you won't get burned by the IRS or pay way too much in taxes. Disclaimer bla bla bla, due diligence, I'm not an accountant, attorney bla bla, etc.