bcmum, thanks for the suggestions. I have done my share of chicken buses. In particular, one in Oaxaca driven by a 13 year old. However, that was when I was much younger and now in my 60s, I find those kind of buses too uncomfortable for my injured lower back to stand more than a couple hours. Just 2 years ago I tried to brave a similar style of bus in Cambodia for a supposed 2.5 hour trip that turned into a nightmare 5 hour trip and it took me 2 days to recover enough to walk around. So we will have to be careful where, when and for how long we take any on this trip.
I am sure we will love Chiapas. In all my many trips to Mexico and living there for 2 years, I have yet to get to that state. So we plan to cross the border and spend awhile traveling there. Given the logistics we will probably be exiting near Comitan and spend a few days there. After Chiapas we will head to Oaxaca. My partner has never been there and I haven't since 1986. Was hoping to travel a bit in Michoacan too an the way up to Puerto Vallarta. We have to be up in Puerto Vallarta by the end of March for our flight back home. However, I think we may not have enough time for Michoacan. We will see.