Starting an one stop shop for people who want to move abroad/migrate and helping them with visa options. Our focus would be investment/startup/skilled/ancestry visas with relocation services + help with taxes. Also how would I monetize this aside from the referral commission cut?
You're asking two questions. On the niche v broad question, I agree with the other posters that going niche is a good strategy. You can carve out a space more easily. That said, it may not be super easy to expand out of a nice once you plant yourself in it. You didn't specify the niche you're exploring so hard to comment beyond that.
As for monetizing, your second question, a couple of things come to mind such as services like relocation, apartment hunt, taxation and financial services. Visa services could be your lead product, with a lot of add ons one you land the customer.