If retiring early isn't the goal, I'd still say to do the 457b, assuming it has good fund options. It gives more flexibility than other account types, plus the tax advantages.
As for taking time off, maybe taxable is the way to go, at least for a year or two worth of replacement income for you--so that you could quit during your DH's sabbatical and not worry about income for a while. Honestly, that sounds pretty awesome. Being able to take time off for yourselves, then have time to look for a job you feel passionate about, would be amazing. A Roth IRA is definitely another good choice, since my understanding is that you can take out contributions without penalty prior to age 59.5. This money could also be used to fund a future house purchase if your DH's job becomes more stable.
The other thing I'd want to make sure you both have is good term life insurance--just in case, and with kids, you need that income replacement. You seem like the type of people to already have this, but if not, term policies for both you and DH would be my suggestion.