I just booked for a party of 9. It was not a problem at all at 60 or 60+ days. At 30 days you will most likely struggle with the super headliners (sdmt fea etc) but everything else shouldn't be a problem. If you run into problems the first thing to attempt is splitting your group into two or three smaller parties and trying to get overlapping times with the intent of riding in the overlap.
Another trick to try is booking for as many as you can and then periodically attempting to add additional members to the existing fp+.
Remember, refreshing your screen or reselecting your time is your friend. This is because when you do a search it temporarily holds the options that it is giving you until you choose one or cancel. This means dozens, hundreds, or even thousands of slots might be temporarily being held by the system, especially during the 30 minutes right after a booking window opens.
Because I had the same questions, I alsi exploted same day availability for a party that size, as well as early/mid afternoon 4th fp+ availability. I found that I saw little or no difference between it and what I was used to for my normal party of 4. Goodluck