What concepts in your learning do you now feel you have a solid grasp on?
I feel that I have a solid grasp on class I weak verbs, as well as class I strong verbs. I also feel that I have a good grasp of the flow of Old-English, which is different from Modern English in that it has less structure. I also feel that my grasp of (Old English) pronouns and different grammatical cases has greatly improved. I am struggling a bit with class II weak verbs as they follow less rules than class one, but I am allowing myself extra time for practice.
Which ones might be helpful for other students in their learning?
Something that is not necessary helpful, but definitely interesting is the connection between Old English and Modern English. For example, our conjugation of past-tense verbs stems directly from the Old English conjugation of the preterite tense. In weak verbs you conjugate the ending with a -de or -te; which is quite similar to our -ed conjugation. Certain exceptions can be explained through Old English as well. In run/ran, that also mirrors the Old English practice of changing internal vowels to conjugate it for preterite tense in strong verbs.