configuration affacting cross-client

Hi Experts

there is a requirement of new company code configuration for same group company but instance will be different under same client. for example, existing client code is 111 now an instance will be created as 222 for new company code.

please let me know what need to be considered / kept in mind considering cross client impact as business scenario of both company is different. e.g. what thing will remain common for both instances i.e. 111 and 222

thanks in advance.