Currently there is no clean way to handle units in default addons values at create time - so we are stuck to different presets for each unit system.
See also this post about units
Archipack 1.4 multi-dimension allow to override scene units on per dimension basis, and also allow to scale text and symbol. (feel free to download the 140_dev branch on github)
On screen manipulators text size is currently hardcoded, should probably allow resize in addon preferences.