No to the first questions. read this to see how to qualify.
https://www.irs.gov/taxtopics/tc429.html
There are pros and cons to switching to an entity and I won't list them all here. From the broker's point of view as you asked, some of the downsides are that:
-you will incur the expense of creating the entity
-you will incur the expense of maintaining the entity (Some states charge an annual fee, your accountant will charge you a little more)
-you will need to maintain a business checking account in the same name and EIN as the entity that might have a monthly cost and will require some balance
-that market data fees will be professional rates vs non-pro rates