You will not get paid during the 3 week course. You are only offered the class if you make it through the hiring process. They want you but want to make sure you make it through ground. Your date of hire is when you get done with 3 week course and check into ground school just like all the other guys showing up for ground. When you get the ground school date they will probably tell you at that time based on your current times.

I start the course on March 3rd.

It is good if you are going to a domicile like BOS since you know your going to the EMB. Someone going to DFW MIA LAX ORD may not be as lucky and go through 36 hours of systems and 20 hours of sim in the ERJ145 then get assigned one of the other aircraft at ground. Good expierence anyway.