not everyone is partnership material, just like not all scientists will win the nobel prize

Currently EY has only 1 KL office - Menara Milenium (MM) at Pusat Bandar Damansara.
The Kompleks Antarabangsa office had closed and the service lines previously located there had shifted to MM.

Only if your investments meet the requirements of the independence policies of the audit firm you are working in. Generally, you and your immediate family members will not be allowed to invest in shares in PLCs (and group of companies under those PLCs) that are clients, regardless of whether or not you are assigned to the team that provide services to these clients.

In many countries such as USA and UK, there are Independence Regulations; Big4 have lots of MNC clients, and the audits of these companies could be subjected to compliance of these regulations.
Example: Audits of MNC with operations/Head Office in USA maybe subjected to the Securities and Exchange Commission's independence requirements (very strict!).

If you wish to know more on this topic, you can always google "Auditor Independence Issues"