The PI or Primary Investigator should be the lead researcher(s) for the project assuming the application wins an SBIR award. The PI is not required to have won previous awards, but credentials and expertise is the area of study is necessary. Depending on the size of the organization, it could be appropriate for the CTO, or even CEO to be listed as a PI ... (more) Letters of support are critical. You should consider them as required.
As the SBIR program is becoming more competitive, you have to assume you are competing against applications that include them - therefore you must as well. As some of the other other answers indicate, these need to be more than just lip service, they should be significant commitmen... (more)