Most poeple don't pay for financial advice because they don't have to. You seem to be targeting people who might really need specialist advice. The difficulty that you might have with only a QFA is in the area of tax advice. Too many investment decisions impacted by their tax effects, If you are charging someone for financial advice you will need to be more than just fairly confident that you can stand over the advice.
As an advisor charging for your advice you will be expected to be able to advise your client on the tax impact of, say, overseas rental income. If you end up in an argument with your client's tax advisor or worse still the client expects you to deal with the Inspector of Taxes when their query relates to the advice you have given you may end up out of your dept, beyond the cover of your professional indemnity insuarance and probably looking at unbillable hours.
As an advisor who is paid by the financial institution then you can wash your hands of this hot potato and advise your client to get some tax advice.