One suggestion: only play six for a good long while. Jumping between 4's, 5's and 6's is baffling (at least to me, and especially starting out). Play the 6 until it feels like "home" and other, less stringed models feel all skinny and weird.
I take a different approach... I teach my students how an instrument is laid out using a 4 string. I show them the relationship of how the instrument is laid out. Once they understand the logical structure, they can seamlessly navigate with intention across a 4, 5, 6, or 7 string instrument.
The only thing that may need to be addressed are muting strategies due to the additional strings.