Californian,
All the best with your plans. There's no reason that you can't handle this for yourselves, as long as you're careful to have all your documents in order. Everyone is under extra stress these days because of covid, so being considerate of that with the people you deal with will serve you well.
To address your concern about document expirations first, your only real concern is the FBI Background Check. The guidance given to the Polícia Federal is that they have discretion to reject any background check older than 90 days. As a practical matter, they'll probably be reasonably understanding if you miss that by a month, or maybe even two. Beyond that, things get progressively riskier.
Several members have reported here that the FBI is turning requests around very quickly, and the Approved Channelers always do. So be strategic. Request your background check about a month before you leave the US: that will leave you time to get it apostilled (US State Department -- there are services that can take care of this for you) and have it when you leave. Schedule your marriage for as soon as you can have it after your arrival in Brazil. Start your application for permanent residency with the Polícia Federal as soon as you have your Brazilian marriage certificate.
Apostilles do not expire, unless the underlying documents do. Documents for one-time events, like birth certificates, marriage certificates, and divorce decrees should not expire; clerks can be officious, but you should be able to jolly them along on this kind of document. Sworn Translations, signed (including electronically) and on the original stationary do not expire.
Here are the general documentation requirements for a cartório marriage of a divorced foreigner in Brazil. Often, a given cartório will have its own little spin on the requirements, so your fiancée should reconfirm with your cartório of choice. If she already has a relationship with the cartório, so much the better:
https://www.casamentocivil.com.br/estra … -no-brasil
"Legalizada" in the context of documents from the United States means the the documents carry apostilles. I've discussed what apostilles are and how to get them on several other threads. If you can't find those discussions, feel free to ask.
Note that, per the list, both your divorce decree and the marriage certificate of your first marriage are required.
Here are the general documentation requirements for permanent residency on the basis of family reunion. Since you're getting married, the ones that apply only to "união estável" don't apply to you:
http://www.pf.gov.br/servicos-pf/imigra … miliar.pdf