Hi Agabby,
I'm replying here as a forum member, not as a developer or official contact person for J51.
Unfortunately, the developer hasn't been active in the forum or anywhere else for quite some time. From what I can see, there's currently no active support, and it's safe to assume that the J51 project has been discontinued or is no longer being maintained.
For this reason, it's very likely that there will be no further changes or enhancements to the shop system, such as the ability to purchase multiple templates in a single transaction.
This is especially unfortunate, as J51 was previously known for its excellent service and support. Many in the forum are very sorry to hear this.
I hope this information helps you with your decision.
Best regards
Marcel