AP Physics 1

I've used Khan videos and problems in the past. I'm considering using it more extensively this year. I've taken the Khan for Educators class and spent time with the first 3 units in AP Physics 1. It's appealing. I like the way content and practice problems are linked, mastery, spiraling, and analytics. Some of the questions I have are on pacing and grading/tests. On pacing, given everything else going on in physics (labs, demos, group work, tests, bridge competitions, ...) it seems that students might have too many assignments if I use most of the Khan material (and will struggle with mastery if I cherry-pick). On tests/grading is best practice to give separate tests, or rely on Khan Unit Tests? What about grading, does the work done on Khan give a basis for grading mastery of the AP Physics 1 content. Input on this or suggestions for how to network with AP Physics 1 teachers using Khan would be appreciated. Thanks.