Do I need updated documents for a 180-day extension on my freelance DTVisa in Thailand?

You will need to show ALL the documentation you showed to get the visa issued, plus proof 500K baht is in your account for a minimum of 30 days before you apply, and all the resident stuff (lease, TM30, previous 90 day report, etc).

At most offices you can apply for an extension when you have 30 days or less left on your current stamp (you don't lose time applying early because the extension is added to your current expiration date)

Go to your immigration office, get the hand out listing the requirements and see if there is anything required that is specific to that office.