Advice for Reconfigure Network Topology

Hello Everyone,

I am a fresh graduate who get a job as a network administrator. I am assigned by my manager to involve in re-engineering company network. I am needed some advices about how our network topology currently running is already appropriate or there should be some changes to better administering in term of performing and security. as a glimpse, here is our network topology.

https://ibb.co/6NxWJJ6

Here is my thought:

- I am thinking about suggesting to add distribution switch to core switch at building A, so VLAN can be managed at distribution level.

- I am thinking about to change VLAN for each building so they have their own VLAN.

- If i change the VLAN, should i keep NX-7K on each building as layer 2 or change it to layer 3 routing ?

Due to my lack of experience i am reluctant to share my thought or give advice to my manager.

any kind of advice or help will be appreciated, and thank you very much.