I usually recommend when doing industry research that you start by finding out what classification number the U.S. Government has assigned to that industry. They collect a lot of data about industries and make it available for free to everyone.
This is the classification system used by the U.S. Government. Use the Search box for the 2012 NAICS on the left to enter in a keyword or two about your industry to find out how they classify it. You will get anywhere from a two-digit (very general) to a six-digit (very specific) classification number. Write this number down. You can use it to search other government sites and business databases to find info on your industry!
The Economic Census is taken every 5 years in years that end in 2 and 7. The most recent census with data available is from 2017. Some top-level data is available now and data will continue to be rolled out over the next few years. This will give you the number of establishments, the value of sales, annual payroll, and number of employees for broad sectors of the U.S. economy. Note that several of the columns report the data in $1,000 of dollars, so you'll need to add 3 zeroes to the end of the number to get the actual dollar value.
In recommended order, here are the databases available to assist you in industry research:
Trade or industry associations are a great source for information on an industry. Some times they have free information available. Other times it is restricted to members of that organization.