The limit of 1000 Maximum URL-patterns mentioned is only for TVP platforms which are SRX1500, SRX4100 and SRX4200. Rest of the devices are non-TVP including SRX340 which have a limit of 50 max url-patterns.
You can the above information in the same KB article you referred to in the post.
TVP has a different architecture differentiating PFE from Junos and additional API compatibility. The above mentioned devices are the only ones with this TVP architecture in SRX.
Regarding the limits, I could not find any documents that mention any numbers but I tried few configurations on the lab device. Tried more than 100 URL entries under a given URL pattern and more than 30 URL patterns under a custom URL category without any issues. The commit was successful atleast.
Hope this helps.
Thanks, Pradeep Please Mark My Solution Accepted if it Helped, Kudos are Appreciated too!!!