Game shows a maximum of 99,999,999,999 of any units can be built at one time. However, in the Queue, you will only end up with 2,147,483,647 of each units under construction.
Following the tick, you then discover that you actually have only 2,126,008,811 of each unit in inventory.
On top of that, no matter what you have built, your NW is maxed out at 2,147,483,647. However, you can try to queue up more units even though your units are already maxed out.
Yes, this is just showing the limits of the number coding within the Test Galaxy and is unlikely to be encountered in any normal galaxy, but figured why not document it here anyway.