I'm building a new project using SEAM 3. I don't understand what the differences between weld archetype and seam forge. Both of them help us to build a simple project template to start with.
The biggest difference is that an archetype is a one time setup, sure it'll give you some very basic code to get you going, but you only use it once.
Forge can be used all the time to help you correctly learn and explore. There are also new plugins coming fairly rapidly with Forge.