I would advise you to get married as soon as you can (as you then have to wait a week or 2 for the marriage certificate to be ready - well at least in California that's how long it took) and like @TBoneTX said to get multiple copies of the marriage certificate (we got 5).
I would also say file to the AOS initially with the strongest case you possibly can within the 90 days. You can then print off and upload additional evidence in between the AOS filing and the interview (if scheduled one).
This is what we submitted initially for evidence along with the AOS paperwork as follows:-
Petitioner (US Citizen) - Proof of US Citizenship (US Passport), Birth Certificate, Most recent federal tax returns, W2's, 1099's, 3 recent pay stubs and 2 passport style colour photographs
Beneficiary - Passport, Birth Certificate, K1 Visa in passport, DS 3025 Vaccination Worksheet (I didn't need to do a new medical exam as I had all required vaccinations at my medical in London last year and my medical was marked as complete so I just provided this and a cover letter explaining this as well), passport style colour photographs, Marriage Certificate, Marriage Proofs - (these can be for example pictures of you both and with family and friends, joint bank accounts, lease agreement, joint health insurance, etc) and SSN and I-94.
**PLEASE NOTE** - All of what we provided in terms of evidence in this filing apart from the passport style colour photographs were copies that were either printed off or scanned and then printed off.
There are also guides on VJ and online if you want to look into those and what you need as well.