Hi all! Thank you for the replies 😁
My fiancé is a U.S. citizen, yes! Regrettably we are too far from Vegas to get there and marry in the next few days. However I have taken your advice and completed all the remaining filing today. The marriage certificate will be the final touch now (except for the medical examination, which I am planning to submit later in the interests of time).
Thanks for this too - I didn’t even consider that we may not receive it the same day! But I have just looked at the NYC website information and fortunately they do indeed provide the certificate at the conclusion of the ceremony, provided that it is held in the City Clerk's Office (which ours will be, thankfully!)
So my plan is to spend the coming days finalizing and printing the complete application, ready to send it off to USCIS on June 6th (the day after we marry) with priority mail. That way they should receive the file before June 10th, I believe. This means that we won’t be able to include honeymoon pictures etc. in our relationship evidence, but hopefully I can provide these at interview, if needed.
Many thanks again for all your help!