Do first semester grades matter if students are applying early action to colleges?

Many colleges, certainly the top 50 schools will require your HS counselor to submit the mid-year transcript to the college. This may or may not have any bearing on whether or not you get accepted. But keep in mind, if you bomb your senior year, they may rescind your admittance and they can do that even after you accept their offer. If you are doing really well, you might want to voluntarily contact them and send them your quarterly report if it has grades on them. That might be helpful especially if you didn't receive any grade Spring semester of Junior year.

To answer your 2nd question, there is nowhere on the Common App to report your grades for 1st semester of Senior year, just a current coursework section where you upload your current classes.

Added from the COMMON APP FAQ about ED/EA:

"You should submit Mid Year Reports as soon as first semester/trimester grades are available. The Common App school forms system does not send reminders about these forms. It is the student's responsibility to keep track of this requirement and ensure that the counselor is aware of it.

The Final Report shouldn't be submitted until the applicant has accepted admission at the school of their choice. Once the Final Report is submitted, you won't be able to submit any of the other forms!

Submitting past a deadline: Some schools may be more lenient with school officials. You will have to contact the school to see if they will accept school forms later than the stated deadline."