I will quickly highlight the faster and simpler way to deal with GU replenishment:
Create a Unit
Create a Series
Place the Unit under the series
Create a Replacement Formation*
Wait for the construction cycle to end
*You need to flag the formation for use as a replacement
If you follow the above steps, every formation with the unit designed that is in need of that specific unit will be replenished by the replacement formation until the formation is empty. Below, you can find some extra information that may not be necessary to achieve what you want.
The template simply tells the game which units are supposed to be part of the specific formation. Personally, I have never changed it since it is by default populated with the same formation. However, if you decide to change the composition of the specific formation and want to change the old ones to new, you may use it. Nevertheless, since the new copy and update feature, I find it even less important. It must be there, though, as it tells the game what to do.
The replacement formation does not need to be the same as the template. For example:
10th Infantry Division2x Infantry Division HQ
1000x Infantry Soldier
100x Infantry Machine Gun
100x Infantry Bazooka
40x Supply Vehicle
Can be resupplied by:
11th Infantry (Soldier Reserve) marked for use as a replacement2x Infantry Division HQ
1000x Infantry Soldier
12th Infantry (Machine Gun Reserve) marked for use as a replacement100x Infantry Machine Gun
13th Infantry (Bazooka Reserve) marked for use as a replacement100x Infantry Bazooka
14th Logistic Division (Reserve) marked for use as a replacement400x Supply Vehicle
You may opt for the simpler version:
11th Infantry Division (Reserve) marked for use as a replacement2x Infantry Division HQ
1000x Infantry Soldier
100x Infantry Machine Gun
100x Infantry Bazooka
40x Supply Vehicle
However, since you may have multiple formations sharing the same units, it could be easier to divide them into groups that can be shipped at the front depending on the assault force composition.
Finally, the most important part of dealing with replenishments is to fully understand the resupply, which requires a constant replenishment of Logistic modules. Ideally, if you use your construction cycle with 5 days, then you need to ensure your main formations can be resupplied for that long (I personally play with construction cycles of 1 day less 1 second).
The long story is available here
https://aurora2.pentarch.org/index.php?topic=8495.msg109760#msg109760 for
resupply and here
https://aurora2.pentarch.org/index.php?topic=8495.msg109786#msg109786 for
combat.
The short version is GSP per round and how many rounds it takes to complete a cycle. You can add a few extra for redundancy if you wish.
1 day: 3 rounds
5 days: 15 rounds
I am sure I may have missed many other important pieces of information that others will be able to debunk/clarify. All I can say is that the above has served its purpose in its current form and keeps things easier for me to manage. You are encouraged to conduct your own research and experimentation to determine what works best for you. This includes adjusting the relative numbers to accommodate any updated rules that I may have missed or that may be updated in the future after this post, as well as aligning with your playstyle. However, the concepts presented appear to be correct in the current state of GU management.