Can overseas income and Hong Kong income be combined with mainland income?
This is possible because the application system has options for different currencies.

Can individual businesses also submit applications?
Of course, you just need to provide complete annual revenue and tax payment proof for more than one year.

Is it necessary to provide a full year's tax payment situation?
If you submit your application in March this year, you can provide the company's or individual's continuous 12 months of revenue and tax payment proof from March last year to February this year.

Is it mandatory to process the ID card within 30 days?
Actually, this is not a strict requirement, just a suggestion. Moreover, now the entire Hong Kong is replacing smart ID cards, and you can hardly make an appointment within a month. Therefore, many people will take more than 30 working days to process their Hong Kong ID after entering the country, which will not affect you at all, nor will it delay your calculation of permanent residency.