Hello @femmepodpresets
Welcome aboard and congratulations for your first approval! Now let’s answer your questions:
Yes, you can change the preview images. Go to your item page → click on the “Edit” tab and go to “Update Item & Tags”. In the “Files” section you will be able to upload your new pictures.
The number can vary depending on the category of the item and the approval ratio of the author. You can see the number of submissions you are allowed per month when you select the category for the item. For more information regarding the approval ratio and submission limits you can check out this thread - > Submission Limits for Graphics
I have seen the other thread you’ve opened before your item got approved and I just wanted to let you know that, for future reference, you can check this link → Envato Marketplace Review Times. However, please note that the times are indicative only, based on the average wait time over the last 7 days. So it might be sooner or later, depending on the amount of files that are waiting for review.
Let me know if you have any other questions. Good luck!