Hello 
I think the most of these available with: groups, categories permission, custom user fields and automation.
To separate users on signup use Discourse Authentication Validations chaining user fields function. So you can show separate user fields depends on what they choose on the first option ( architect or laypeople. )
After this, with Discourse Automation you can automatically add these users to the expected group.
For example:
| User Field Option | Group |
|---|---|
| architect → | architect |
| laypeople → | laypeople |
Finally set up the categories permissions for these groups.
- architect group can see architect and laypeople categories
- laypeople group can see laypeople categories
Something like this maybe can help and add some idea. 