Thank you! I wish I would've known you had replied so long ago! Is there a way to receive a notification to a post on this forum (I hope so, that would be most convenient), or do I just need to check back regularly to see if you've replied? 

That's a great question! Grading proofs are tricky. Here's some guidance:

If a proof is worth four points on a test, I give one point for writing the "given" statements along with the reason "Given." Easy point!

Then, I divide the points up among the remainder of the proof. For example, if you miss one reason, it would be half a point off, as long as the rest of your proof is solid.  

If you start off going the right way, but then the proof just goes awry and has too many holes in it for it to make sense, then I would likely deduct two points.