As a general rule, keep business and personal separate. Litigation/creditors issues would be the big one. Longevity, the investment company might last 30-40 years, while you may want to close down the business company after trading stops (litigation issues again). Sale or business partners, I might want half of your business, so I buy some share off you, but I don't want your investments, so you would need to make changes to clean the company prior to sale.
BTW - this is all general advice, doesn't take into account your personal situation. I assume as you already this far along this path, any DIV 7A or PSI issues are consider factored into your choices.
