Custom Gradebook questions: function vs. form advice sought

[a61morris]

I am a language teacher, and our official gradebook software is cumbersome and unreliable. I am trying to customize a worksheet to serve as backup for the official online book (because it has limited features, and has lost scores for me).

The most important part of this (attempted) solution is to store comments alongside the scores for assignments. This feature is very limited in the official software. The comments are essential.
The ultimate goal of this worksheet is to store grades and comments so that I have a full picture of grades and extenuating circumstances, for each student on each assignment.
I would LIKE to have the math working too, so that I can have all my info available on one platform (with the eventual goal to possibly be able to generate reports/mail merge...).

So the attached worksheet shows my visual goal, with a place for scores and a comment possible for each score.

My questions are as follows:
1. How weird is it going to be to get the computations done with the comments "in the way?" I'm not sure how to handle the numbers/text format difference.

2. The other hurdle is how to create a formula to read the value of the relevant cell in Row 3 and count the assignment ONLY for the appropriate category (so the D column would hold the average of all Writing Assignments (designated by a W in row 3), Column E would be Reading, designated by R, etc.)

3. Have I made a fundamental error in how I have set this up?

I appreciate you taking a look, and any advice you might be able to share.