Inversions in Functional Harmony

I would approach it like this:

1. The progression can be written without necessarily thinking about the inversion as long as you are moving from left to right. The inversions of the I6 and IV6 chords are specific instances where the chart moves back to the left from the right along arrows.
2. Once you’ve written the progression, go back through and try to create an interesting bass line. The easiest way to do this, is to identify other chord tones that can move by step into the next chord. For instance, if you have a progression – I-V-I, you could easily change the bass note of the V chord to a D, and the 2nd I chord to an E. This bassline would work because everything remains functional, and the bass moves in a smooth way.
3. Don’t go overboard, keep some roots in the bass, keep some leaps, and mix in steps.

Generally, if you are just learning functional harmony, I would stick with mostly roots in the bass for now. Once you feel you “get it” then start playing around with different basslines.