How can I improve my table design for different types of an entity?
Sorry, but is an entrepreneur not also an individual? You should record the name etc. in individual, then the additional info in another table. Now you may have one person double. And stuff like address should be linked to "entity" - not even client, you may end up having suppliers there too.

The "Data Model Resource Book" has perfect diagrams for address and contact handling including relationships of entities with each other. There is a lot of detail issues you get seriously wrong in your approach.