What a "right of first refusal" clause does (and keep in mind you can have your attorney craft it however you like, so these are just basic guidelines) is say that if for any reason one parent can't care for the children during "their time," the other parent needs to be offered the opportunity to step in before a third-party caregiver could be brought in.
When exes get along and live nearby, "right of first refusal" usually works out well with or without a formal clause--after all, most parents welcome the opportunity to spend more time with their kids (and they do also have the right to say no to the extra time if they have a conflict). Plus, it saves the other parent money on a sitter. People who get along tend to be reasonable and understand that the spirit of "right of first refusal" doesn't mean that Grandma can't take the kids out to a movie.
It's when there's animosity that those clauses can be problematic. Parents end up ignoring the clause completely, or taking their ex-spouse back to court because the ex dropped the kids off at a birthday party, or wanting to enforce the clause for a 15-minute trip to the store while the stepparent or older sibling is right there.
As for leaving the state, I only have experience on the refusal side, but 90 miles isn't that far (we're 70 miles from my stepdaughter's mother and we see my SD every week), and if you can show your motives are reasonable, you are willing to help your kids maintain a relationship with their dad, and so forth, you will be in a better position to get court approval than, say, moving 1,000 miles into the home of an alcoholic and a convicted sex offender (as in the refusal case I'm familiar with).
ProtoLawyer (the now-actual lawyer, this isn't legal advice, please don't take legal advice from some anonymous yahoo on the Internet)
Spouse (the political geek) * Stepdaughter (the artist) * and introducing...the Baby (um, he's a baby? He likes shiny things).