The starting templates are just that;
DUPLICATES are great for test-beds for experimental designs, to see how ORG, HA, SA, Piercing, work between each other ; and
1] when introducing new templates, keep an eye on your stockpiles, to be able to have the needed equipment for your new division [XX] template ;
2] be sure of the new battalion(s) [BNs] BEFORE you hit the 'save' button ;
3] most additions to a basic template will be INCREMENTAL, a BN here, another BN there; depending upon your stockpiles .
These should be FIELD PROMOTIONS, so you upgrade a small number of XXs as affordable; rather than doing the entire damn ARMY, in one fell swoop !!
I remember, as USSR, at around 250 hours into the game, to add 2 line AA BNs to the basic 9 INF/0 Arty XX {{before I found out about duplicates}} ;
BOY-HOWDY, did I goof THAT up, I had 195 XXs of 9/0s at the time when I hit the 'save' button ... and it took me 2 YEARS to claw my way out of the production pit !
'Stair-stepping' improves a XX by adding 1-2 BNs per template, while aiming at a larger XX, like a 13 INF/ 4 Arty/ 2 AA (+supports) XX, in several steps .