When should go to Entreprise Architecture?

Hi, we have 4 differents plants and for now we’re planning to have 4 standard architectures. Theses are not big plants and we just start to use Ignition. For the biggest plant we can have maybe 19000 tags.

I was thinking we can eventually switch to an entreprise architecture when all 4 plants SCADA will be more developped.

Do you think is it a good approach? Should we start with entreprise architecture first?